Remove Game::shouldreturntopausemenu

This kludge variable was used to re-set the warp background after coming
back from the in-game settings menus. But since #522 got merged, this
has no longer been necessary.

desktop_version/src/Logic.cpp

@@ -87,16 +87,6 @@ void maplogic()
     graphics.updatetextboxes();
     graphics.updatetitlecolours();
 
-    if (game.shouldreturntopausemenu)
-    {
-        game.shouldreturntopausemenu = false;
-        graphics.backgrounddrawn = false;
-        if (map.background == 3 || map.background == 4)
-        {
-            graphics.updatebackground(map.background);
-        }
-    }
-
     graphics.crewframedelay--;
     if (graphics.crewframedelay <= 0)
     {