Revert of AudioPlayer: Start playing a track when play icon on the track list is clicked.

Revert of AudioPlayer: Start playing a track when play icon on the track list is clicked. (patchset #3 id:40001 of https://codereview.chromium.org/1431523003/ )

Reason for revert:
We decided to punt redesign of audio player to M49.

Original issue's description:
> AudioPlayer: Start playing a track when play icon on the track list is clicked.
>
> Clicking a track usually changes tracks but doesn't change the play state. (play / pause)
> With this CL, clicking play icon which is shown on hover will force start playing the track.
>
> BUG=488229
> TEST=manually
>
> Committed: https://crrev.com/38df7abb0c59ef1ea11cc183ae151b6c235ff4c9
> Cr-Commit-Position: refs/heads/master@{#357071}

TBR=yawano@chromium.org
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=488229
Committed: https://crrev.com/f44eb9893d0b73bdb1501012bb46922c32b310bb
Cr-Commit-Position: refs/heads/master@{#359285}

[fukino, 2015-11-12 08:30:36]

Created Revert of AudioPlayer: Start playing a track when play icon on the track
list is clicked.

[commit-bot: I haz the power, 2015-11-12 08:30:43]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1435223003/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1435223003/1

[commit-bot: I haz the power, 2015-11-12 08:31:20]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1435223003/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1435223003/1

[commit-bot: I haz the power, 2015-11-12 08:32:00]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-11-12 20:06:00]

Patchset 1 (id:??) landed as
https://crrev.com/f44eb9893d0b73bdb1501012bb46922c32b310bb
Cr-Commit-Position: refs/heads/master@{#359285}