Delete unused RcsMessage code for now.

This feature is incomplete and will be worked on later. For now
since it uses hidden APIs its better to delete it.

Test: basic sanity
Bug: 140908357
Merged-in: I4a11d5440dca1b98275bfd2b18f3ef5dae65e95a
Change-Id: I4a11d5440dca1b98275bfd2b18f3ef5dae65e95a
(cherry picked from commit db6aa1a4)