rpcgen: Don't free() a pointer after realloc().

A successful realloc() already frees the old pointer.

Reported by:	GCC -Wuse-after-free
Reviewed by:	brooks, imp, emaste
Differential Revision:	https://reviews.freebsd.org/D37540

usr.bin/rpcgen/rpc_main.c

@@ -925,7 +925,6 @@ moreargs(void)
 		warnx("unable to allocate arglist");
 		crash();
 	}
-	free(arglist);
 	arglist = newarglist;
 }