Do not restrict the allowed signals that can be specified by number

to the list of signals that has symbolic name. It was impossible to
send rt signals with kill(1) due to the check.

MFC after:	1 week

bin/kill/kill.c

@@ -108,7 +108,7 @@ main(int argc, char *argv[])
 			numsig = strtol(*argv, &ep, 10);
 			if (!**argv || *ep)
 				errx(1, "illegal signal number: %s", *argv);
-			if (numsig < 0 || numsig >= sys_nsig)
+			if (numsig < 0)
 				nosig(*argv);
 		} else
 			nosig(*argv);