CameraITS: cleanup preview stabilization tests

This CL addresses some comments from the original CL:
- Use its_session_utils.ANDROID13_API_LEVEL constant instead of an
  internal constant.
- f-strings were not printing messages correctly when used with
  `skip_unless`, replaced with `.format` instead.

Bug: 211806326
Test: python tests/sensor_fusion/test_preview_stabilization.py -c config.yml
      python tests/scene4/test_preview_stabilization_fov.py -c config.yml
      Ensured that the tests skip as expected with the right message.
Change-Id: Ic2a26fe5a7dd52de5b0a99d1822227bf3c48403b
2 files changed