Bug 31667: Merge 'tip' and 'hint' classes

Bug 31667: Merge 'tip' and 'hint' classes

This patch corrects a few instances of the use of the "tip" class and
replaces them with "hint." The patch also removes the class from the
staff interface CSS.

To test, apply the patch and rebuild the staff interface CSS.

- View a patron account and click the "Routing lists" link in the
  left-hand sidebar.
  - On the subscription routing lists page the "Search subscriptions"
    page label should look correct.
- Go to Reports -> Catalog by item type.
  - The "Select none..." hint should be styled correctly.
- The third instance, in the installer, is only visible if you try to
  install Koha using a MySQL user who doesn't have the correct
  privileges, so may be too much trouble to really test. A check of the
  patch should be adequate.

Signed-off-by: Fridolin Somers <fridolin.somers@biblibre.com>
Signed-off-by: Katrin Fischer <katrin.fischer@bsz-bw.de>
Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>