Fix potential NPE when connecting

In one case NPE could be caused by a callback in MediaResumeListener
setting the browser to null. However the code for this can be simplified

- Move disconnect() calls to ResumeMediaBrowser where possible
- Remove callback that is now unnecessary
- Also, the controller commands in MediaResumeListener were redundant since
ResumeMediaBrowser already handles restarting playback

Fixes: 183122550
Test: atest MediaResumeListenerTest ResumeMediaBrowserTest
Change-Id: I7cbde108b4bedcd6e22e08c59af83ef42b586dd4