[Fortran] Remove OpenACC 'loop' inside 'parallel' special-case code

Instead, use the generic middle-end code, like already used for Fortran OpenACC
'loop' inside other compute constructs, orphaned 'loop' constructs, and C, C++
generally.

	gcc/fortran/
	* openmp.c (oacc_is_parallel, resolve_oacc_params_in_parallel):
	Remove.
	(resolve_oacc_loop_blocks): Don't call the former.
	gcc/testsuite/
	* gfortran.dg/goacc/loop-2-parallel-3.f95: Adjust.