math.h: remove unneeded math.h includes

sys/net/routing/rpl/trickle.c

@@ -19,7 +19,6 @@
 #include <string.h>
 #include <stdio.h>
 #include <stdlib.h>
-#include <math.h>
 
 #include "inttypes.h"
 #include "trickle.h"

sys/net/transport_layer/destiny/socket.c

@@ -16,7 +16,6 @@
  */
 
 #include <inttypes.h>
-#include <math.h>
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>

sys/net/transport_layer/destiny/tcp_timer.c

@@ -15,7 +15,6 @@
  * @}
  */
 
-#include <math.h>
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>