BtHelper: clean HFP device connection

Do not report an error when disconnecting or connecting the same
HFP device twice a this causes a mismatch between BtHelper and
AudioDeviceInventory.
Optimize HFP device disconnection by only disconnecting the relevant
audio device type when known.
Also improve log for SCO audio state changes in dumpsys.
Also cleanup @GuardedBy annotations in BtHelper

Bug: 348265701
Test: make
Flag: EXEMPT bug fix.
Change-Id: Icfa9acd8497e087430442cf299ecb75d5c9b14d3