Unsharing a file does not trigger a delete event on the sharee device

[pmarini-nc]

1. user1 shares a file with user2
2. without a polling event the file is synced in user2 desktop
3. user1 unshares the file
4. the file is not deleted from user2 desktop. Only a polling event deletes the file.

Environment: Desktop Client: 3.7.1 Server: 25.0.3 notify_push: 0.5.2