If an object is anchored to a cell, then it is expected that
this object belongs to this cell and it's survive after a
deletion of the cell makes no sense. So the anchored object
will be deleted together with the cell. Objects anchored to
the page are not affected.

Change-Id: I91f24bf92ab5329aba1d053b3cf5fba77bf16e4f
Reviewed-on: https://gerrit.libreoffice.org/69390
Tested-by: Jenkins
Reviewed-by: Eike Rathke <erack@redhat.com>