Update primary key in VIS sound model database.

The public API for getting at KeyphraseSoundModels is based on the user,
locale, and keyphrase ID. However, the sound model database would allow
multiple models to be registered using the same values, as it has a
primary key on the model UUID. This can potentially lead to a scenario
where multiple models are enrolled for the same user, and the data that
is returned when querying models is arbitrary.

V6 of the sound model database now enforces a primary key over the user
ID, locale and keyphrase ID. When inserting a new model with the same
primary key, the old model will be removed and the new model will be
used instead.

When upgrading from V5 to V6, if there are any models that would violate
the primary key constraint, they are all dropped.

Bug: 32174118
Change-Id: I9597c6a994f01a426625c3be2c53e826f26f5156