SI-7592 Deprecate s.c.m.DefaultMapModel

“This class is used internally.” — No, it isn't.
It isn't used anywhere else either and it doesn't add much benefit,
considering that it lacks documentation and has no tests at all.
Merge pull request #2751 from soc/SI-7592-defaultmapmodel

SI-7592 Deprecate s.c.m.DefaultMapModel