refactor(android): review `KMManager.KMDefault_UndefinedPackageID`

@mcdurdin commented in #16146:

> I know this isn't new, I really wonder about the whole `KMDefault_UndefinedPackageID` (aka `"cloud"`) pattern throughout this code. It seems like this is a fake "null" but I haven't fully audited its use. I would love to eliminate it altogether (28 references) because it seems like it is unnecessary complexity.

(https://github.com/keymanapp/keyman/pull/16146/changes#r3489879917)

and

> Ah, now I understand `KMManager.KMDefault_UndefinedPackageID`. It's legacy from before we had packages. I wonder how many people still have a version of Keyman installed that has these legacy bits. I am guessing near zero. It might be worth adding a Sentry info report on startup telling us whether each user has legacy data.
>
> If we get no positive reports then we can just strip this out entirely.

(https://github.com/keymanapp/keyman/pull/16146/changes#r3489929891)