revert (hack style) fix to clean up invisible cubes

This fix is no longer needed, because the new corner handling in the
physics engine does no longer care about those cubes. Also, they can
now be cleaned up by mapmrproper.

source/src/world.cpp

@@ -62,11 +62,7 @@ void remip(const block &b, int level)
             r->floor = floor;
             r->ceil = ceil;
         }
-        if(r->type==CORNER)
-        {
-            if(!editmode) loopi(4) { o[i]->floor = r->floor; o[i]->ceil = r->ceil; }   // do the physics engine a favour and have the map data reflect what is actually rendered ;)
-            goto mip;                       // special case: don't ever split even if textures etc are different
-        }
+        if(r->type==CORNER) goto mip;                       // special case: don't ever split even if textures etc are different
         r->defer = 1;
         if(SOLID(r))
         {