Removes and returns the first element of this queue.
The queue must not be empty when this method is called.
Source
E removeFirst() {
if (_head == _tail) throw IterableElementError.noElement();
_modificationCount++;
E result = _table[_head];
_table[_head] = null;
_head = (_head + 1) & (_table.length - 1);
return result;
}