do not save UNO marks in undo history

These are usually very short-lived marks that are used for various
internal purposes or by UNO interfaces, so restoring them from undo history
does not make any sense. It can in fact lead to a crash on undo if the mark has
been already deleted (which is usually the case with UNO marks) but
the restoring still refers to it (this is not a problem with other mark types
since those should be deleted only when they are no longer in the document,
in which case they are saved in undo history by content positions rather than
mark references).

Change-Id: Id707dc3d2b888b5c96a974d04a0ef17b22fc024c