remove now unused dialog

Change-Id: I42c340a6aee016e37ee558d46a8eab101837e9c5
Reviewed-on: https://gerrit.libreoffice.org/10074
Reviewed-by: Caolán McNamara <caolanm@redhat.com>
Tested-by: Caolán McNamara <caolanm@redhat.com>