Revert workaround to fix playing songs at specific index

[luizgrp]

After androidx/media#85 gets fixed and media3 dependency is updated in the project, revert changes made in #497 that are a workaround for this issue:

• mediaIndexToSeekTo and onTimelineChanged should be removed;
• calls to seekTo, prepare and play should be made by setMediaListAndPlay;

As alternative, function setMediaListAndPlay should be removed and a setMediaList(mediaList, index) added instead. setMediaListAndPlay is taking care of playing at the moment to avoid having clients to code a "delay" call as per in #494

[fstanis]

As of #646, reverting these two things in PlayerRepositoryImpl.kt:

• Remove private fun updateTimeline
• Remove EVENT_TIMELINE_CHANGED from eventHandlers

[luizgrp]

androidx/media#85 was fixed in 1.0.0-beta03, this can be reverted as we are already using that version.