patch/gfx: Remove non working window mode feature

This wasn't worked as intended since the beginning. There was also
an issue that actually raised a discussion about this and clarified
that it's not that easy under linux unfortunately.

src/main/hook/patch/gfx.h

@@ -9,9 +9,4 @@
  */
 void patch_gfx_init();
 
-/**
- * Force the game into window mode
- */
-void patch_gfx_force_window_mode();
-
 #endif