Revert of Intorduce PowerButtonObserver API

Revert of Intorduce PowerButtonObserver API (patchset #3 id:80001 of https://codereview.chromium.org/654343002/)

Reason for revert:
This is breaking the main waterfall : http://build.chromium.org/p/chromium.chromiumos/builders/Linux%20ChromiumOS%20Tests%20(1)

It appears that athena_unittests got added to the waterfall and not trybots. Please fix that before relanding this.

Original issue's description:
> Intorduce PowerButtonObserver API
>
> renamed existing PowerButtonController to ShutdownDialog
>
> BUG=None
> TEST=covered by unit tests
>
> Committed: https://crrev.com/0d921cdf45872ebff6c22da6a21c12d44054a860
> Cr-Commit-Position: refs/heads/master@{#299821}

TBR=mukai@chromium.org,oshima@chromium.org
NOTREECHECKS=true
NOTRY=true
BUG=None

Committed: https://crrev.com/6c29a291f248469a892233e008d3d6568efd6191
Cr-Commit-Position: refs/heads/master@{#299846}

[jam, 2014-10-16 04:52:17]

Created Revert of Intorduce PowerButtonObserver API

[commit-bot: I haz the power, 2014-10-16 04:53:16]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/659923002/1

[commit-bot: I haz the power, 2014-10-16 04:54:04]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2014-10-16 04:54:40]

Patchset 1 (id:??) landed as
https://crrev.com/6c29a291f248469a892233e008d3d6568efd6191
Cr-Commit-Position: refs/heads/master@{#299846}