Remove visual noise from UnoControls

Change-Id: I0ffbc08cf769e39e8c3b7519e8d2e13ccbe6e3d8
Reviewed-on: https://gerrit.libreoffice.org/8331
Reviewed-by: Caolán McNamara <caolanm@redhat.com>
Tested-by: Caolán McNamara <caolanm@redhat.com>