clean up doxygen errors introduced by new metaprograms

Description

The new metaprograms introduced recently introduced a host of doxygen warnings:

stan/math/rev/fun/multiply.hpp:545: warning: argument 'm1' of command @param is not found in the argument list of stan::math::multiply(const Mat1 &A, const Mat2 &B)

The symbol m1 doesn't even show up in that file. There are also lots of problems with scalars. In total:

$ make doxygen
mkdir -p doc/api
doxygen doxygen/doxygen.cfg
/Users/carp/cmdstan/stan/lib/stan_math/stan/math/prim/fun/acos.hpp:45: warning: argument 'x' from the argument list of stan::math::acos has multiple @param documentation sections
/Users/carp/cmdstan/stan/lib/stan_math/stan/math/prim/fun/asin.hpp:43: warning: argument 'x' from the argument list of stan::math::asin has multiple @param documentation sections
/Users/carp/cmdstan/stan/lib/stan_math/stan/math/prim/fun/atan.hpp:41: warning: argument 'x' from the argument list of stan::math::atan has multiple @param documentation sections
/Users/carp/cmdstan/stan/lib/stan_math/stan/math/prim/fun/ceil.hpp:37: warning: argument 'x' from the argument list of stan::math::ceil has multiple @param documentation sections
/Users/carp/cmdstan/stan/lib/stan_math/stan/math/prim/fun/cos.hpp:40: warning: argument 'x' from the argument list of stan::math::cos has multiple @param documentation sections
/Users/carp/cmdstan/stan/lib/stan_math/stan/math/prim/fun/cosh.hpp:39: warning: argument 'x' from the argument list of stan::math::cosh has multiple @param documentation sections
/Users/carp/cmdstan/stan/lib/stan_math/stan/math/prim/fun/distance.hpp:31: warning: argument 'x1' of command @param is not found in the argument list of stan::math::distance(const T1 &v1, const T2 &v2)
/Users/carp/cmdstan/stan/lib/stan_math/stan/math/prim/fun/distance.hpp:31: warning: argument 'x2' of command @param is not found in the argument list of stan::math::distance(const T1 &v1, const T2 &v2)
/Users/carp/cmdstan/stan/lib/stan_math/stan/math/prim/fun/exp.hpp:43: warning: argument 'x' from the argument list of stan::math::exp has multiple @param documentation sections
/Users/carp/cmdstan/stan/lib/stan_math/stan/math/prim/fun/fabs.hpp:37: warning: argument 'x' from the argument list of stan::math::fabs has multiple @param documentation sections
/Users/carp/cmdstan/stan/lib/stan_math/stan/math/prim/fun/floor.hpp:37: warning: argument 'x' from the argument list of stan::math::floor has multiple @param documentation sections
/Users/carp/cmdstan/stan/lib/stan_math/stan/math/prim/fun/inv_cloglog.hpp:78: warning: argument 'x' from the argument list of stan::math::inv_cloglog has multiple @param documentation sections
/Users/carp/cmdstan/stan/lib/stan_math/stan/math/prim/fun/inv_sqrt.hpp:39: warning: argument 'x' from the argument list of stan::math::inv_sqrt has multiple @param documentation sections
/Users/carp/cmdstan/stan/lib/stan_math/stan/math/prim/fun/inv_square.hpp:22: warning: argument 'x' from the argument list of stan::math::inv_square has multiple @param documentation sections
/Users/carp/cmdstan/stan/lib/stan_math/stan/math/prim/fun/log.hpp:45: warning: argument 'x' from the argument list of stan::math::log has multiple @param documentation sections
/Users/carp/cmdstan/stan/lib/stan_math/stan/math/prim/fun/log10.hpp:38: warning: argument 'x' from the argument list of stan::math::log10 has multiple @param documentation sections
/Users/carp/cmdstan/stan/lib/stan_math/stan/math/fwd/fun/log_softmax.hpp:23: warning: argument 'x' from the argument list of stan::math::log_softmax has multiple @param documentation sections
/Users/carp/cmdstan/stan/lib/stan_math/stan/math/fwd/fun/log_sum_exp.hpp:54: warning: argument 'x' from the argument list of stan::math::log_sum_exp has multiple @param documentation sections
/Users/carp/cmdstan/stan/lib/stan_math/stan/math/prim/fun/logit.hpp:86: warning: argument 'x' from the argument list of stan::math::logit has multiple @param documentation sections
/Users/carp/cmdstan/stan/lib/stan_math/stan/math/prim/fun/mdivide_left_tri.hpp:59: warning: argument 'A' from the argument list of stan::math::mdivide_left_tri has multiple @param documentation sections
/Users/carp/cmdstan/stan/lib/stan_math/stan/math/rev/fun/multiply.hpp:545: warning: argument 'm1' of command @param is not found in the argument list of stan::math::multiply(const Mat1 &A, const Mat2 &B)
/Users/carp/cmdstan/stan/lib/stan_math/stan/math/rev/fun/multiply.hpp:545: warning: argument 'm2' of command @param is not found in the argument list of stan::math::multiply(const Mat1 &A, const Mat2 &B)
/Users/carp/cmdstan/stan/lib/stan_math/stan/math/rev/fun/multiply.hpp:545: warning: argument 'm1' of command @param is not found in the argument list of stan::math::multiply(const Mat1 &A, const Mat2 &B)
/Users/carp/cmdstan/stan/lib/stan_math/stan/math/rev/fun/multiply.hpp:545: warning: argument 'm2' of command @param is not found in the argument list of stan::math::multiply(const Mat1 &A, const Mat2 &B)
/Users/carp/cmdstan/stan/lib/stan_math/stan/math/prim/fun/round.hpp:36: warning: argument 'x' from the argument list of stan::math::round has multiple @param documentation sections
/Users/carp/cmdstan/stan/lib/stan_math/stan/math/prim/fun/sinh.hpp:37: warning: argument 'x' from the argument list of stan::math::sinh has multiple @param documentation sections
/Users/carp/cmdstan/stan/lib/stan_math/stan/math/prim/fun/sqrt.hpp:37: warning: argument 'x' from the argument list of stan::math::sqrt has multiple @param documentation sections
/Users/carp/cmdstan/stan/lib/stan_math/stan/math/prim/fun/square.hpp:51: warning: argument 'x' from the argument list of stan::math::square has multiple @param documentation sections
/Users/carp/cmdstan/stan/lib/stan_math/stan/math/prim/fun/sum.hpp:37: warning: argument 'm' of command @param is not found in the argument list of stan::math::sum(const T &v)
/Users/carp/cmdstan/stan/lib/stan_math/stan/math/prim/fun/tan.hpp:39: warning: argument 'x' from the argument list of stan::math::tan has multiple @param documentation sections
/Users/carp/cmdstan/stan/lib/stan_math/stan/math/prim/fun/tanh.hpp:39: warning: argument 'x' from the argument list of stan::math::tanh has multiple @param documentation sections

Current Version:

v3.1.0