Method _stopReceiving

src/cdk/drag-drop/drop-list-ref.ts:755–759

* Called by a connected drop list when dragging has stopped. * @param sibling Sibling whose dragging has stopped.

(sibling: DropListRef)

   * @param sibling Sibling whose dragging has stopped.
   */
  _stopReceiving(sibling: DropListRef) {
    this._activeSiblings.delete(sibling);
    this._viewportScrollSubscription.unsubscribe();
    this.receivingStopped.next({initiator: sibling, receiver: this});
  }

  /**
   * Starts listening to scroll events on the viewport.