BluetoothHearingAid#getHiSyncId now consistently uses the term HiSyncId

(removed all references to CustomerId) and added link to explain what
the HiSyncId represents

Bug: 149238489
Test: Manual
Merged-In: I4ff2a8d46f3fc5d06a29829a69a27a0c15e466f8
Change-Id: I4ff2a8d46f3fc5d06a29829a69a27a0c15e466f8