[CtsSensorPrivacyTestCases] Change some asserts to assumes

If the device is unable to lock then we should skip these tests since
the intent of this test is to only cover SensorPrivacy APIs and
the coverage has already been lost due to inability to prepare the
device correctly.

Change-Id: Ida2e878bedf487f748c81dc85dfe616a6602518e
Test: atest CtsSensorPrivacyTestCases
Bug: 308362870