Camera Extensions - Remove fallback logic for Get

- get API had fallback logic to rely on camera2 cameracharacteristics
  value if the value associated with the key was not present
- this can potentially introduce inconsistencies and incorrect results
- it's more correct to not fallback
- ensure that when the interface does support the get api it doesn't
  return an empty / null set

Test: atest
Bug: 323626521
Change-Id: I20a31bc1cbc1a668bb228f270fee3b377a3c0093