Deprecate MediaExtractor.setMediaCas

- There is no evidence of usage, after
  checking with all known stakeholders.
- We are aware of bugs that were never
  detected by users (b/193267732).
- The successor (MediaCasV2) is already available
  as a system API (under android.media.tv.tuner,
  including the Descrambler class).

Deprecation has a role in the long term MediaExtractor
codebase convergence.

Test: Built the tree.
Bug: 201414083
Change-Id: If7a6f160a007ab2db9e55a1ad003a948e6668b58