Allow buffer removal when MediaSource is ended
Created by: epiclabsDASH
Fix #2415 (closed).
In some situations, like when there are track changes, we have to allow the buffer to be removed even when it has reached the end of the stream. This PR adds the possibility of indicating to SourceBufferController that a buffer must be removed, independently of the playback context, and use it to force removal of buffers when there are track switches.