Fix issues with multiple languages and multi-users

For multi-user the issue was looking into the user ID of the current
process instead of the active user. The current process was the system
process and the call to UserManager was returning a user handle that
wasn't of any use while trying to map sound models to a user.

For language, the issue was that we were incorrectly just looking up the
model based on the keyphrase id, however we should have also taken the
enrolled model's locale into account.

Explicitly document that for model management the string representation of locales
is a BCP47 language tag.

Remove debug logging.

Bug: 16798166
Bug: 17462570
Bug: 17463511
Change-Id: Ieffb3e218de63f6e7f40af9705dced481a35b0ad