nptl: Remove tst-cancel-wrappers test and related macros

With upcoming BZ#12683 fix, syscall cancellation is not more handled
by {libc,pthread,librt}_{enable,disable}_asynccancel symbols.  This renders
both LIBC_CANCEL_HANDLED and empty declaration and tst-cancel-wrappers.sh
unrequired.  This patch removes both the macro and the nptl test.

Checked on x86_64-linux-gnu.

	* io/creat.c (LIBC_CANCEL_HANDLED): Remove macro.
	* io/ppoll.c (LIBC_CANCEL_HANDLED): Likewise.
	* misc/pselect.c (LIBC_CANCEL_HANDLED): Likewise.
	* nptl/pthreadP.h (LIBC_CANCEL_HANDLED): Likewise.
	* sysdeps/generic/sysdep-cancel.h (LIBC_CANCEL_HANDLED): Likewise.
	* sysdeps/mach/hurd/sysdep-cancel.h (LIBC_CANCEL_HANDLED): Likewise.
	* sysdeps/posix/pause.c (LIBC_CANCEL_HANDLED): Likewise.
	* sysdeps/posix/sigpause.c (LIBC_CANCEL_HANDLED): Likewise.
	* sysdeps/unix/sysv/linux/creat.c (LIBC_CANCEL_HANDLED): Likewise.
	* sysdeps/unix/sysv/linux/creat64.c (LIBC_CANCEL_HANDLED): Likewise.
	* sysdeps/unix/sysv/linux/sigwait.c (LIBC_CANCEL_HANDLED): Likewise.
	* sysdeps/unix/sysv/linux/sigwaitinfo.c (LIBC_CANCEL_HANDLED):
	Likewise.
	* nptl/Makefile [$(run-built-tests) = yes] (tests-special): Remove
	tst-cancel-wrappers.sh.
	(generated): Remove tst-cancel-wrappers.out.
	(tst-cancel-wrappers.out): Remove rule.
	* nptl/tst-cancel-wrappers.sh: Remove file.