MediaRouter: Clean up resources

- Remove resources which are unused or doesn't have opposite
  theme resources in the same density.
- Rename 'cast' to 'mr'.
- Remove redundant use of media_route.
- Rename on/off to connected/disconnected.

Bug: 29232660
Change-Id: I4e09703b3b383c4282a6fd08a7ad9a846de3cde1
337 files changed