Remove <string.h> #include from main.cpp

We no longer use libc string functions, instead preferring SDL's; this
unused include should be removed.

desktop_version/src/main.cpp

@@ -1,6 +1,5 @@
 #include <SDL.h>
 #include <stdio.h>
-#include <string.h>
 
 #include "editor.h"
 #include "Enums.h"