Bug 24405: Make OPAC link underlining consistent

Bug 24405: Make OPAC link underlining consistent

This patch makes a minor modification to the OPAC CSS so that links are
consistently displayed without underlines in their inactive state. This
corrects two cases: Links in the facets sidebar and "Check all/none"
links shown on search results.

To test, apply the patch and rebuild the OPAC CSS
(https://wiki.koha-community.org/wiki/Working_with_SCSS_in_the_OPAC_and_staff_client).

- In the OPAC, perform a search.
- In the search results facets sidebar, confirm that links are not underlined.
- At the top of the search results table, confirm that the "Select all"
  and "Clear all" links are not underlined.

Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>