Fix Preprocessor check for Leader Keys

quantum/process_keycode/process_leader.c

@@ -17,9 +17,7 @@
 #ifdef LEADER_ENABLE
 
 #include "process_leader.h"
-#ifdef __arm__
-#   include <string.h>
-#endif
+#include <string.h>
 
 #ifndef LEADER_TIMEOUT
   #define LEADER_TIMEOUT 300