[flang][fir] Redundant DeclareOps for assumed rank arrays.

Consider the following fortran code.

```
program main
implicit none
integer :: d0,d1(3),d2(3,3),d3(3,3,3)
d0 = 5
d1 = 6
d2 = 7
d3 = 8
print *, mean(d0)
print *, mean(d1)
print *, mean(d2)
print *, mean(d3)

contains

function mean(x) result(y)
integer, intent(in) :: x(..)
integer :: y
select rank(x)
rank(0) ; y = 0
rank(1) ; y = rank(x)
rank(2) ; y = rank(x)
rank(3) ; y = rank(x)
rank default ; y = 100
end select

end function mean

end program main

```

generate the fir using the following command

`flang -fc1 -emit-mlir test.f90 -mmlir -mlir-print-debuginfo -debug-info-kind=standalone -O0`

You will notice that it has around 6 `declare.op` for variable `x` which is an assumed rank array. We end up generating multiple entries for this in the debug information which is not only waste of space but also confuses the debugger.