Remove stale Autoconf checks for Perl

Subversion r110220 (Git commit 03b8fe49) for
PR25884 "libgomp should not require perl to compile" removed all '$(PERL)'
usage from libgomp -- but didn't remove the then-unused Autoconf Perl check
itself.  Later, this Autoconf Perl check appears to have been copied from
libgomp into other GCC libraries, likewise unused.

	libgomp/
	* configure.ac (PERL): Remove.
	* configure: Regenerate.
	* Makefile.in: Likewise.
	* testsuite/Makefile.in: Likewise.
	libatomic/
	* configure.ac (PERL): Remove.
	* configure: Regenerate.
	* Makefile.in: Likewise.
	* testsuite/Makefile.in: Likewise.
	libgm2/
	* configure.ac (PERL): Remove.
	* configure: Regenerate.
	* Makefile.in: Likewise.
	* libm2cor/Makefile.in: Likewise.
	* libm2iso/Makefile.in: Likewise.
	* libm2log/Makefile.in: Likewise.
	* libm2min/Makefile.in: Likewise.
	* libm2pim/Makefile.in: Likewise.
	libitm/
	* configure.ac (PERL): Remove.
	* configure: Regenerate.
	* Makefile.in: Likewise.
	* testsuite/Makefile.in: Likewise.