No longer bind to gatt from BluetoothManagerService

Having or not a gatt service is now consider as a implementation detail.

----

Previous Behavior:
1. Bind to AdapterService(mBluetooth)
2. adapter.enable -> bringUpBle() -> StartService(Gatt)
3. After start is done, trigger state_change callback with BLE_ON
4. BMS bind to Gatt and then start brEdr if needed

Between 3 and 4, listener of BLE_STATE_CHANGED intent may expect
getBluetoothGatt to return a non-null token

Current Behavior:
1. Bind to AdapterService(mBluetooth)
2. adapter.enable -> bringUpBle() -> BindService(Gatt)
3. After bind is done, trigger state_change callback with BLE_ON
4. BMS start brEdr if needed

Bug: 262605980
Bug: 285959170
Test: atest ServiceBluetoothTests
Test: manual start & stop of Bluetooth
Change-Id: I1aef0faa84d9f465239a05731e740c34df38e753