QS: fix filtering additional tiles

- TILES_AVAILABLE should be filtered instead of TILES_DEFAULT
  (broken in Ia92e562318c05a127ddccc99dc7461feaa7ed9cb)
- tiles.remove(tileKey) is not needed since the remove is done by
  iterator.remove()
- Remove TILES_DEFAULT since it is no longer used

Change-Id: I77804f4eb821cab4edfa90d71dfa0b4fae9bcf31