Fix update cleanup to only affect file and folders

Fix bug in the SQL query that cleans up stray shares for removed
files/folders, which is now correctly limited to that item type instead
of also removing all other share types.

Related to https://github.com/owncloud/core/pull/7293

Please review @MorrisJobke @schiesbn @DeepDiver1975 @icewind1991 

Something to keep in mind: when writing test it's always better to add a few extra cases to simulate unrelated data, and assert that the data still exists.