Bluetooth API: Do not allow apps to programmatically make BT discoverable.

Instead add ACTION_REQUEST_DISCOVERABLE for the system to show a dialog to
adjust discoverable mode.

Also remove createBond(), removeBond() and cancelBondProcess(). The Settings
App already handles these automatically when connections require bonding.

Change-Id: I216154cd1b6de410de64ba91b07d7263ac03e8df