Use existing middle end checking for Fortran OpenACC loop clauses

Use existing middle end checking for Fortran OpenACC loop clauses

Don't duplicate in the Fortran front end what's generically being checked in
the middle end.

	gcc/fortran/
	* openmp.c (resolve_oacc_loop_blocks): Remove checking of OpenACC
	loop clauses.
	gcc/testsuite/
	* gfortran.dg/goacc/loop-2-kernels.f95: Update.
	* gfortran.dg/goacc/loop-2-parallel.f95: Likewise.
	* gfortran.dg/goacc/nested-parallelism.f90: Likewise.

From-SVN: r266922