sparc: bury a zombie extern that had been that way for twenty years

Back in January 1998, in 2.1.79 check_pending() got taken out and shot.
Users in arch/sparc and arch/sparc64 got converted away from it.  One
of the externs (in arch/sparc) was taken out at the same time.  Two
other (in arch/sparc64/kernel/sys_sparc{,32}.c) got stuck.  The one in
sys_sparc32.c was quietly removed 6 years later by an unrelated
commit.  The last one kept shambling until now.  It's time to end
that depravity, let's bury the body...
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

arch/sparc/kernel/sys_sparc_64.c

@@ -523,8 +523,6 @@ asmlinkage void sparc_breakpoint(struct pt_regs *regs)
 	exception_exit(prev_state);
 }
 
-extern void check_pending(int signum);
-
 SYSCALL_DEFINE2(getdomainname, char __user *, name, int, len)
 {
         int nlen, err;