Changes

[1/7] personalization: refactor: drop ClassVarMeta use

Drop the ClassVarMeta/metaclass/ABCMeta stuff -- it doesn't seem to
serve any purpose that is not similarly achieved with plain python
inheritance.

Upcoming patches will use normal inheritance a lot more.

Note that most use of the ClassVarMeta was in the SdKey subclasses, and
that these currently don't actually work. See the fix in patch
I07dfc378705eba1318e9e8652796cbde106c6a52 .

Related: SYS#6768
Change-Id: I60ea8fd11fb438ec90ddb08b17b658cbb789c051