Revert "gtbs: Add Generic Telephone Bearer Service implementation"

Revert submission 1873900-gtbs

Reason for revert: broke cellular call over BT, see b/213412267
Reverted Changes:
I284ddacfc:gtbs: Add Generic Telephone Bearer Service impleme...
I8264ade4b:gtbs: Add Generic Telephone Bearer Service support...
I996cd5ff9:Add support for Generic Telephone Bearer service (...

Bug: 213412267
Tag: #feature
Test: answer cellular call by pressing button on HFP headset
Change-Id: Iee09b21d21e4d0a6478c98434acc123a5c8c5bb3