[std] 'subclause \\ref' cleanups

As a follow up to #3354 and its resolving PR, grepping for 'subclause \ref' reveals:

algorithms.tex:the algorithms specified in this subclause \ref{specialized.algorithms}
concepts.tex:The concepts in subclause \ref{concepts.callable} describe the requirements on function
expressions.tex:considered further according to the rules in subclause \ref{expr.compound};
numerics.tex:Throughout this subclause \ref{rand},
numerics.tex:Throughout this subclause \ref{rand},
numerics.tex:Throughout this subclause \ref{rand},
numerics.tex:of this subclause \ref{rand.req.seedseq}.
numerics.tex:of this subclause \ref{rand.req.eng}.
numerics.tex:of this subclause \ref{rand.req.dist}.
numerics.tex:In this subclause \ref{rand},
support.tex:For the purposes of subclause \ref{cmp.categories},
utilities.tex:For the purposes of subclause \ref{smartptr},
utilities.tex:Each specialization of a class template specified in this subclause \ref{func.search}

If "this subclause" is really the current subclause, then the \ref is redundant and should be dropped to be consistent with 147 other "this subclause". Also, for these and capital Subclause, a ~ is inconsistently placed between subclase and \ref. I don't know what that does, though. I suppose it makes the text a single entity for some purpose.

Start by grepping the listed .tex files for “subclause \ref” and compare those matches with the 147 existing “this subclause” uses. Read the surrounding text to determine whether each reference names the current subclause, and investigate the existing ~ placement before making consistent wording changes. Done means the redundant references and inconsistent spacing are resolved across algorithms.tex, concepts.tex, expressions.tex, numerics.tex, support.tex, and utilities.tex.