recog/reload: Remove old UNARY_P operand support

reload and constrain_operands had some old code to look through unary
operators.  E.g. an operand could be (sign_extend (reg X)), and the
constraints would match the reg rather than the sign_extend.

This was previously used by the MIPS port.  But relying on it was a
recurring source of problems, so Eric and I removed it in the MIPS
rewrite from ~20 years back.  I don't know of any other port that used it.

Also, the constraints processing in LRA and IRA do not have direct
support for these embedded operators, so I think it was only ever a
reload-specific feature (and probably only a global/local+reload-specific
feature, rather than IRA+reload).

Keeping the checks caused problems for special memory constraints,
leading to:

	  /* A unary operator may be accepted by the predicate, but it
	     is irrelevant for matching constraints.  */
	  /* For special_memory_operand, there could be a memory operand inside,
	     and it would cause a mismatch for constraint_satisfied_p.  */
	  if (UNARY_P (op) && op == extract_mem_from_operand (op))
	    op = XEXP (op, 0);

But inline asms are another source of problems.  Asms don't have
predicates, and so we can't use recog to decide whether a given change
to an asm gives a valid match.  We instead rely on constrain_operands as
something of a recog stand-in.  For an example like:

    void
    foo (int *ptr)
    {
      asm volatile ("%0" :: "r" (-*ptr));
    }

any attempt to propagate the negation into the asm would be allowed,
because it's the negated register that would be checked against the
"r" constraint.  This would later lead to:

    error: invalid 'asm': invalid operand

The same thing happened in gcc.target/aarch64/vneg_s.c with the
upcoming late-combine pass.

Rather than add more workarounds, it seemed better just to delete
this code.

gcc/
	* recog.cc (constrain_operands): Remove UNARY_P handling.
	* reload.cc (find_reloads): Likewise.