sidebar: remove alignment handlers

from paragraph panel

Change-Id: I46cc0c81df02cba681a0586a7ef859f77be046c6
Reviewed-on: https://gerrit.libreoffice.org/8045
Reviewed-by: Caolán McNamara <caolanm@redhat.com>
Tested-by: Caolán McNamara <caolanm@redhat.com>