Batch delete on shared with me page must decline all shares

[PVince81]

Steps

1. Create two users "user1" and "user2"
2. Login as "user1"
3. Create three folders "accepted", "pending", "rejected"
4. Share all three with "user2"
5. Login as "user2"
6. Go to the "shared with me" page. All three shares appear pending.
7. For "accepted" click on "Accept"
8. For "rejected" click on "Decline"
9. Refresh the page
10. Select all three shares with the top checkbox
11. Click "Delete" on the top bar to batch delete

Expected result

All shares are now declined

Actual result

Errors occur because the wrong request is sent: a Webdav DELETE is sent instead of an OCS Share API call for declining. This is because the batch delete button uses the code path for file deletion.

Need to branch the code path to use the share API when batch declining.

Version

master (actually found on #3049)