fdo#78903: Don't broadcast prematurely during cell deletion.

We need to wait until all the affected cells get marked dirty at the
end of the deletion process.

Change-Id: I49618fcc386ec2209f5f0267d50257ecb8dd21d1
(cherry picked from commit cb167ac784f9b16944da4494b65e56b2a5b66bb7)
Reviewed-on: https://gerrit.libreoffice.org/9443
Reviewed-by: Eike Rathke <erack@redhat.com>
Tested-by: Eike Rathke <erack@redhat.com>