remove unused SDL2/SDL.h and physfs.h from twn_util.h, explicit usage of SDL in apps, move to Scancode enum in apps

apps/scenery/scenes/ingame.c

@@ -6,6 +6,9 @@
 
 #define STB_PERLIN_IMPLEMENTATION
 #include <stb_perlin.h>
+#include <SDL2/SDL.h>
+
+#include <stdlib.h>
 
 
 static void ingame_tick(State *state) {

apps/scenery/scenes/title.c

@@ -4,6 +4,7 @@
 #include "twn_game_api.h"
 
 #include <stdio.h>
+#include <stdlib.h>
 
 
 static void title_tick(State *state) {