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/Game.cpp

@@ -7232,7 +7232,6 @@ void Game::returntopausemenu()
     ingame_titlemode = false;
     returntomenu(kludge_ingametemp);
     gamestate = MAPMODE;
-    map.kludge_to_bg();
     graphics.titlebg.tdrawback = true;
     graphics.backgrounddrawn = false;
     mapheld = true;