移除relibc和old libc以及旧的shell (#529)

移除relibc和old libc以及旧的shell

user/apps/test_signal/main.c

@@ -17,13 +17,11 @@
  *
  */
 
-#include <math.h>
 #include <signal.h>
-#include <stdio.h>
-#include <stdlib.h>
-#include <time.h>
-#include <unistd.h>
 #include <stdbool.h>
+#include <stdio.h>
+#include <unistd.h>
+
 bool handle_ok = false;
 int count = 0;
 void handler(int sig)