Add tests for OCP\Share::unshareAll().
OCP\Share::unshareAll(): Deduplicate hook parameters.
Extract unshare() code into unshareItem().
Use unshareItem() in unshareAll().
Use unshareItem() when unsharing expired shares.
Deduplicate expiration date check into a method.
Always select item_source.
Merge pull request #4961 from owncloud/unshare-over-delete

Use OCP\Share::unshare() instead of directly using OCP\Share::delete()