Remove bogus include of strings.h

The tests include strings.h but don't need any of its functions

server/tests/basic_event_loop.c

@@ -1,7 +1,6 @@
 #include <stdlib.h>
 #include <stdio.h>
 #include <sys/time.h>
-#include <strings.h>
 #include <signal.h>
 #include <string.h>
 

server/tests/test_empty_success.c

@@ -1,5 +1,4 @@
 #include <stdlib.h>
-#include <strings.h>
 #include <spice.h>
 
 SpiceTimer* timer_add(SpiceTimerFunc func, void *opaque)

server/tests/test_just_sockets_no_ssl.c

@@ -1,4 +1,3 @@
-#include <strings.h>
 #include <sys/select.h>
 #include <spice.h>
 #include "basic_event_loop.h"

server/tests/test_playback.c

@@ -1,5 +1,4 @@
 #include <stdio.h>
-#include <strings.h>
 #include <sys/select.h>
 #include <sys/time.h>
 #include <math.h>