Remove kludge_to_bg() and bg_to_kludge()

Now that tower, title, and horizontal/veritcal warp backgrounds all use
separate buffers, there's no longer any need to temporarily store
variables as a workaround for the buffers stepping on each other.

desktop_version/src/Input.cpp

@@ -2379,7 +2379,6 @@ void mapmenuactionpress()
         {
             game.createmenu(Menu::options);
         }
-        map.bg_to_kludge();
         game.kludge_ingametemp = game.currentmenuname;
 
         graphics.titlebg.scrolldir = 0;