Move "return to editor" alpha timer update to logic functions

Otherwise it'll go by too quickly.

Also something subtle here - I didn't make it conditional on
game.advancetext, so now it'll still decrement even if you have
advancetext up.

desktop_version/src/Render.cpp

@@ -1390,9 +1390,6 @@ void gamerender()
      if(map.custommode && !map.custommodeforreal && !game.advancetext){
         //Return to level editor
         graphics.bprintalpha(5, 5, "[Press ENTER to return to editor]", 220 - (help.glow), 220 - (help.glow), 255 - (help.glow / 2), ed.returneditoralpha, false);
-        if (ed.returneditoralpha > 0) {
-            ed.returneditoralpha -= 15;
-        }
       }
 #endif