remove unused SIGTIMER handler in timer_create

this was leftover from when the actual SIGEV_THREAD timer logic was in
the signal handler. commit 5b74eed3b301e2227385f3bf26d3bb7c2d822cf8
replaced that with use of sigwaitinfo, with the actual signal left
blocked, so the no-op signal handler was no longer serving any
purpose.

the signal disposition reset to SIG_DFL is still needed, however, in
case we inherited SIG_IGN from a foreign-libc process.

src/time/timer_create.c

@@ -32,15 +32,10 @@ static void cleanup_fromsig(void *p)
 	longjmp(p, 1);
 }
 
-static void timer_handler(int sig, siginfo_t *si, void *ctx)
-{
-}
-
 static void install_handler()
 {
 	struct sigaction sa = {
-		.sa_sigaction = timer_handler,
-		.sa_flags = SA_SIGINFO | SA_RESTART
+		.sa_handler = SIG_DFL,
 	};
 	__libc_sigaction(SIGTIMER, &sa, 0);
 }