Don't add toolkit related shell packages with headless build

Change-Id: Ib68bf02ef7065c76ff25f36b8c29a9a4b028b2e0
Reviewed-on: https://gerrit.libreoffice.org/12268
Reviewed-by: Michael Stahl <mstahl@redhat.com>
Tested-by: Michael Stahl <mstahl@redhat.com>