Deprecate internal ORMTable::unprefixFieldName(s)

unprefixFieldNames is not used anywhere outside of the class. Why
should it?

unprefixFieldName became unused in I19194f1, but I did not removed
it because it is public.

The fact that both methods are public is a mistake as far as I can
tell. I can't think of a good reason to do that.

Change-Id: Iafc527b5d534648a962a8c2015d21403362bb573
Merge "Deprecate internal ORMTable::unprefixFieldName(s)"