removeChild = (parent, child, prevProp = '_prev', nextProp = '_next') => {
  const prev = child[prevProp];
  const next = child[nextProp];
  prev ? prev[nextProp] = next : parent._head = next;
  next ? next[prevProp] = prev : parent._tail = prev;
  child[prevProp] = null;
  child[nextProp] = null;
}
@param  {Object} parent
@param  {Object} child
@param  {String} [prevProp]
@param  {String} [nextProp]
@return {void}