A few locking changes

1. The Monitor class was essentially doing nothing because the scoped_lock objects weren't actually locking any supplied mutex.  Also, locking before a function call is a bad idea because the bounds of the lock are indeterminate, so do not lock there anymore.
2. Remove the writeMutex_ in WebRtcConnection; it was only protecting a single method that doesn't need protection
3. Remove some unused stuff.