When an app tried to re-prepare a live streeam with server side inserted
ad after a playback exception, the player tried to find the ad group by
its index in the ad playback state of the next timeline when creating
the first period.
If a source that supports server side ad, has removed the ad playback
state when the source has been removed, this causes a crash. For live
streams this is a reasonable thing to do given the exception could be
caused by an invalid ad playback state.
This change removes the ad metadata from the current period for live
streams and the timeline. In case the ad playback state is not reset
by the source, the first timeline refresh would ad the metadata again.
PiperOrigin-RevId: 541959628
(cherry picked from commit 207ef0d0f0bee86e75409f53ded325e859ca25aa)
