rhbz#1030009 Remove global XModel ref

...that is apparently effectively unused since
2627bdaddc6f694dc7fc6ba347a305af0f88ee2c "INTEGRATION: CWS fwk02ea: #i28639#
always used supplied status indicator" anyway but causes crashes during exit
when it holds an SwXTextDocument ref.

Change-Id: I542545c793855b41731de72650bf07d5748fcb9f
(cherry picked from commit a7464edb0a4368db02b1298b5710cf98b17e282b)
Reviewed-on: https://gerrit.libreoffice.org/6804
Reviewed-by: Michael Stahl <mstahl@redhat.com>
Tested-by: Michael Stahl <mstahl@redhat.com>