The problem is that sw::UpdateFramesForAddDeleteRedline() sends a
SwFormatFieldHintWhich::REMOVED event in order to remove any comments
that may have been deleted from the document view.

Unfortunately there's another listener in class FieldDocWatchingStack
that is used during various SwPostItMgr::Delete* functions, which will
effectively start over from scratch if it receives this event, so it
is an infinite loop.

Avoid this by simply ignoring any redline-deleted fields; deleting them
again won't provide any benefit anyway.

This can be seen with UITest
deleteAllComments.DeleteAllComments.test_comment_trackchanges.

(regression from 9b67b6a6)

Change-Id: Ie1d5676d1d79a51e2e4a01a3e282f8739ff08899
Reviewed-on: https://gerrit.libreoffice.org/66178
Tested-by: Jenkins
Reviewed-by: Michael Stahl <Michael.Stahl@cib.de>