Remove useless #ifdefs from Linux sig*.c syscalls

Remove useless #ifdefs from Linux sig*.c  syscalls

sigprocmask.c, sigtimedwait.c, sigwait.c and sigwaitinfo.c files from
sysdeps/unix/sysv/linux include nptl-signals.h via nptl/pthreadP.h,
and so SIGCANCEL and SIGSETXID become defined unconditionally. But
later in the code, there are some checks weither symbols defined,
which is useless. This patch removes useless checks.

Checked on x86_64-linux-gnu.

	* sysdeps/unix/sysv/linux/sigprocmask.c: Remove useless #ifdefs.
	* sysdeps/unix/sysv/linux/sigtimedwait.c: Likewise.
	* sysdeps/unix/sysv/linux/sigwait.c: Likewise.
	* sysdeps/unix/sysv/linux/sigwaitinfo.c: Likewise.

Signed-off-by: Yury Norov <ynorov@caviumnetworks.com>
Reviewed-by: Andreas Schwab <schwab@suse.de>
Reviewed-by: Adhemerval Zanella <adhemerval.zanella@linaro.org>