fdo#62082 Fix buttons in Custom animation toolbar

* Use small button size
* Fix duplicate arrows
* Change "Remove" icon
* Remove no longer used icons

Change-Id: I28a22704fc0696d00d97ac3b6b6fc0c98c3433ed
Reviewed-on: https://gerrit.libreoffice.org/7867
Reviewed-by: Caolán McNamara <caolanm@redhat.com>
Tested-by: Caolán McNamara <caolanm@redhat.com>