Bug 8085: Follow-up: Update to 'Hold Slip' for existing installations

Bug 8085: Follow-up: Update to 'Hold Slip' for existing installations

Title and description are updated separately, in case that the
library has changed one of them when editing the slip.

To test:
- Verify that you have a letter named 'Reserve Slip' in your database
- Run the database update
- Verify the slip has been renamed correctly

Signed-off-by: Frédéric Demians <f.demians@tamil.fr>
  Job done on a Koha English version. It won't hurt other langages

Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>
Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>