Revert "Keep mingw specific includes ifdef'd"

This reverts commit ba8b9ae307.

Turns out this is needed on other systems, just happened to be indirect included on them.

source/blender/blenlib/intern/rand.c

@@ -33,10 +33,7 @@
 #include <stdlib.h>
 #include <string.h>
 #include <math.h>
-
+#include <time.h>
-#ifdef __MINGW32__
-#  include <time.h>
-#endif
 
 #include "MEM_guardedalloc.h"