Bug 6885 Allow superlib to delete items from any library

Bug 6885 Allow superlib to delete items from any library

When IndependantBranches syspref is enabled, a 'regular' user can only
delete items belonging to his/her library. But a superlibrarian should
have the permission to delete items from all libraries. He can't for the
time being. This is fix by this patch.

How to test?

- On a multi-libraries Koha, activate IndependantBranches
- Log in with a superlibrarian user
- Find a biblio with one item from another library than the user home
  library
- Click on Edit > Edit Items
- On the list of items, all lines have Delete link
- If you try to delete an item from another library than the user home
  library, deletion will fail.

Signed-off-by: Owen Leonard <oleonard@myacpl.org>
Signed-off-by: Paul Poulain <paul.poulain@biblibre.com>
Signed-off-by: Chris Cormack <chrisc@catalyst.net.nz>