Fix EZP-20728: eZRest v2 : Some (unknown) REST call corrupts the database and make MoveSubtree call fail

This PR fixes issue https://jira.ez.no/browse/EZP-20728

This fixes a bug where removing aliases for a deleted subtree where another subtree was previously moved out of also removed active autogenerated aliases of a previously moved subtree.

## Additional

Removing aliases no longer converts them to NOP entries but deletes them completely, same as in LS.
This was done in difference to how LS works, in order to prevent destroying custom aliases when a Location that uses a part of custom alias path is removed.

The problem with this was that when moving a subtree to a new Location where corresponding NOP entries already exist (up to 2nd level or deeper) reparenting would fail as id (parent, text_md5) was already occupied.

The problem still exists with NOP entries that are part of custom alias path. This is a design limitation and is inherited from legacy database structure. The fix for this in the worst case scenario would require publishing aliases of all Locations in a moved subtree and would be too complex and resource demanding.