LP#1981095: fix deletion of item tags in Angular item attributes editor

LP#1981095: fix deletion of item tags in Angular item attributes editor

This patch fixes several bugs that prevent item tags from
being correctly deleted by the Angular item attributes editor.

To test
-------
[1] Apply patch.
[2] Edit a single item in the Angular item attributes editor.
[3] Verify that tags can be added and deleted.
[4] In Holdings View, choose Add/Manage Item Tags for a single
    selected item.
[5] Verify that tags can be added and deleted;
[6] Repeat steps 4 and 5 for a different item after successfully
    deleting an item tag. Verify that tags can be added and deleted.
[7] In Holdings View, choose Add/Manage Item Tags for multiple
    selected items.
[8] Verify that ntoes can be added to the selected items

Signed-off-by: Galen Charlton <gmc@equinoxOLI.org>
Signed-off-by: Bill Erickson <berickxx@gmail.com>