sigprocmask()' man page references sigmask()' in synopsis.

Note odd `sigmask()' line in synopsis.  `sigsetops(3)' is better suited
for `sigprocmask' and is already referenced from the manual page.
(`sigmask()' is useful for the older (& deprecated) `sigsetmask()' API).
PR:		6395
Reviewed by:	phk
Submitted by:	Joseph Koshy <koshy@india.hp.com>

lib/libc/sys/sigprocmask.2

@@ -41,7 +41,6 @@
 .Fd #include <signal.h>
 .Ft int
 .Fn sigprocmask "int how" "const sigset_t *set" "sigset_t *oset"
-.Fn sigmask signum
 .Sh DESCRIPTION
 The
 .Fn sigprocmask