Returned it back.
Added deprecation warning.
Example:
````python
test_unlock_to_camera_with_passcode (test_lockscreen_unlock_to_camera_with_passcode.TestCameraUnlockWithPasscode) ... /home/sasha/GitProjects/gaia/tests/python/gaia-ui-tests/gaiatest/tests/functional/lockscreen/test_lockscreen_unlock_to_camera_with_passcode.py:24: Warning: Class "LockScreen" is deprecated and soon will be removed. Please use corresponding methods of "GaiaDevice" class
  self.device.lock()
/home/sasha/GitProjects/gaia/tests/python/gaia-ui-tests/gaiatest/tests/functional/lockscreen/test_lockscreen_unlock_to_camera_with_passcode.py:32: Warning: Class "LockScreen" is deprecated and soon will be removed. Please use corresponding methods of "GaiaDevice" class
  self.assertTrue(self.device.is_locked)
expected failure
````