Bug 12267: Remove borrower_attributes.password

Bug 12267: Remove borrower_attributes.password

When creating a patron attribute type, there is a "Allow password"
checkbox. If checked, the librarian will be able to enter a password for
this patron attribute when editing a patron.
The goal was to allow a patron to log in with a secondary password.
However, this feature has never been implemented.

"""
commit 6fc62bcd321eddb0fd3ae46903e9ab6c8b1db2cd
  CommitDate: Mon May 12 09:03:00 2008 -0500
  extended patron attributes tables & syspref (DB rev 081)

- password_allowed (if set, staff patron editor will
  allow a password to be associated with a value; this
  is mostly a hook for functionality to be implemented
  in the future.
"""

To decrease maintainability, this patch suggest to remove the 2 DB fields
borrower_attributes.password and
borrower_attribute_types.password_allowed
If they have not used by the library.

Test plan:
- Edit a patron attribute type and select "allow password"
- Edit a patron and defined a password for this attribute
- Execute the DB entry
- Note that you get a warning
- Empty the password field
- Execute the DB entry
- You do not get the warning and the 2 DB fields have been removed

Signed-off-by: Marc Veron <veron@veron.ch>
Signed-off-by: Marcel de Rooy <m.de.rooy@rijksmuseum.nl>
Signed-off-by: Brendan Gallagher <brendan@bywatersolutions.com>