PBAP: remove dead code

* SocketAcceptThread, and its helper method initSocket(),
closeServerSocket(), are never used.
* Private method setUserTimeoutAlarm() is never used.
* Private fields mRemoveTimeoutMsg, mPermission, mSdpSearchInitiated,
mIsRegisteredObserver are never used.

Bug: 69417672
Test: Test with carkits supporting PBAP. Functioinality should be
unchanged.

Change-Id: I8a0051dbf3e80e9b1c873fd38b97d88e5cfc5dec