sub-task of bug 264134 Whenever a method is called in the SourceBufferPrivate, the value of MediaSource::isEnded() is passed. But the MediaSourcePrivate was already notified that the MediaSource has been ended and each SourceBufferPrivate keep a reference to the MediaSourcePrivate. So we can simplify the code and remove some unnecessary methods.
<rdar://problem/117899460>
Pull request: https://github.com/WebKit/WebKit/pull/19940
Committed 270390@main (b21ca9944221): <https://commits.webkit.org/270390@main> Reviewed commits have been landed. Closing PR #19940 and removing active labels.