CtsCameraTestCases: Clean up FeatureCombinationTest

This patch cleans up some code in FeatureCombinationTest. Specifically
it:
1. Reduces nesting / simplifies logic to make it easier to follow
2. Uses the appropriate expect* methods to ensure the error messages
   are appropriate, and the intent explicit.
3. Runs the linter to appease the lint gods.

Bug: n/a
Test: atest CtsCameraTestCases: FeatureCombinationTest passes.
      No functional change.
Change-Id: I0ddf2876dfdc3cb40b351f6ae1033ad090d8ca74