Refactor/make game vars extern (#451)

* Remove GameVariables pointer for callbacks

* Make game_vars a global

* move declaration of game vars in header

* Move g_game_vars location

include/splash_screen.h

@@ -7,8 +7,6 @@
 #ifndef SPLASH_SCREEN_H
 #define SPLASH_SCREEN_H
 
-#include "game.h"
-
 #include <tonc.h>
 
 /** @name Splash screen timing variables
@@ -25,16 +23,16 @@
 /**
  * @brief Initialize the splash screen by printing the splash screen text.
  */
-void splash_screen_on_init(GameVariables* vars);
+void splash_screen_on_init(void);
 
 /**
  * @brief Update splash screen timers and print the remaining time accordingly.
  */
-void splash_screen_on_update(GameVariables* vars);
+void splash_screen_on_update(void);
 
 /**
  * @brief Exit the splash screen
  */
-void splash_screen_on_exit(GameVariables* vars);
+void splash_screen_on_exit(void);
 
 #endif // SPLASH_SCREEN_H