HFP: Disable BTRH feature

Fluoride does not notify application layer upon AT+BTRH, and always
sends error response (BTRH is not supported) to remote device.
That is, Fluoride does not support BTRH feature.
But BTRH is enabled by default, so OK is sent to remote device by mistake
before the error response is sent. This makes some carkits unstable.

Bug: 29587048
Test: make, PTS test

Change-Id: If1aa32291491982851ecd480c4ba8390f39a27a2
Merged-In: If1aa32291491982851ecd480c4ba8390f39a27a2
(cherry picked from commit a25ef0b60b4ca10385dac02334dc3e4e2ad23edb)