Special levels: mkmap roomno cleanup and room removal after map

mkmap creates mines-style full-level maps, so it should wipe
out all the room numbers in the level away. Also, it uses
temporary rooms for making sure the map is fully joined together;
those temporary rooms were left on the map, but should've
been cleared away.

When putting down map-parts on the level, don't remove the room
data which would be under that map; the map may have holes in them
(using the "x" map char), so a room may still exist there.
I don't think it matters if there is any room data which doesn't
have any room numbers referring to it in the level.
(Usually the special levels use map right after level_init anyway,
so there wouldn't be any rooms in the level)

src/sp_lev.c

@@ -6649,9 +6649,6 @@ TODO: g.coder->croom needs to be updated
                 else if (splev_init_present && levl[x][y].typ == ICE)
                     levl[x][y].icedpool = icedpools ? ICED_POOL : ICED_MOAT;
             }
-        if (g.coder->lvl_is_joined && !g.in_mk_themerooms)
-            remove_rooms(g.xstart, g.ystart,
-                         g.xstart + g.xsize, g.ystart + g.ysize);
     }
 
  skipmap: