code: func (s *Store) RemoveCollection(name string) {
  	for {
  		orig := atomic.LoadPointer(&s.coll)
  		coll := copyColl(*(*map[string]*Collection)(orig))
  		cold := coll[name]
  		delete(coll, name)
  		if atomic.CompareAndSwapPointer(&s.coll, orig, unsafe.Pointer(&coll)) {
  			cold.closeCollection()
  			return
  		}
  	}
  }
docs: // The Collection removal won't be reflected into persistence until
  // you do a Flush().  Invoking RemoveCollection(x) and then
  // SetCollection(x) is a fast way to empty a Collection.