Refine Bluetooth silence mode API

- Remove silence state extra data from ACTION_SILENCE_MODE_CHANGED
  intent
- Rename getSilenceMode -> isInSilenceMode
- Throw IllegalStateException if Bluetooth is not enabled

Bug: 124448652
Test: runtest bluetooth

Change-Id: I6a8d8d848249faaac34e87408dcf750073b03584
2 files changed