Bug 31803: "remove from cart" button displayed even if not in cart

Bug 31803: "remove from cart" button displayed even if not in cart

This patch modifies CSS related to the "Remove from cart" button
associated with bibligraphic record views. A change in specificity of
buttons made by Bug 30952 made it so that the button was no longer
hidden correctly.

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

- Locate a bibliographic record in the staff interface and view the
  detail page.
- In the toolbar you should see an "Add to cart" button but not a
  "Remove from cart" button.
- The buttons should correctly toggle on and off as you add and remove
  the title from the cart.

Signed-off-by: David Nind <david@davidnind.com>
Signed-off-by: Katrin Fischer <katrin.fischer@bsz-bw.de>
Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>