Prevent phone's bd_addr from appearing in Accounts

Bluetooth's pbapclient needs to create an Account to help manage the
syncing of phonebook contacts and call logs. This Bluetooth-generated
Account will show up in Settings > Accounts, leading to a confusing and
poor user experience. This CL will prevent this Account from appearing.

This fix relies on the fact that getAccountPreferences in
AccountListPreferenceController will skip showing any Account that has a
null 'label'.

Bug: 131857089
Test: Verify in Settings > Accounts that the phone's bd_addr is no
longer listed.

Change-Id: I31dec95f3cd2d66f2f1b1c9bf80cb9c3031b585b
Merged-In: I31dec95f3cd2d66f2f1b1c9bf80cb9c3031b585b
(cherry picked from commit 8ff121fc)