Clear up ALWAYS_REPORTED_SIGNAL_STRENGTH_CHANGED in BT pkg

The feature "alwasy report signal strength" has been obsoleted and
in clearing up. Client should switch to new public API
TelephonyManager#setSignalStrengthUpdateRequest.

Bug: 177924721
Fix: 203460567
Test: atest HeadsetPhoneStateTest
Change-Id: I8fc98a57c85d94e3cb3930459569d309bad33641