fdo#74687: Undo & redo of format-only changes don't need broadcasting.

Also discovered that the undo path was broadcasting twice.  Let's only
do it once.

Change-Id: I169f1659aecb1eb78be3a497e244f79c5883e50f
(cherry picked from commit 1d1fbbe81b4435765d3f69c6bcae2840dc629912)
Reviewed-on: https://gerrit.libreoffice.org/9075
Tested-by: Markus Mohrhard <markus.mohrhard@googlemail.com>
Reviewed-by: Markus Mohrhard <markus.mohrhard@googlemail.com>