Revert of CQ to always post a message when Commit box is unchecked.

Revert of CQ to always post a message when Commit box is unchecked. (https://codereview.chromium.org/138173005/)

Reason for revert:
This created a lot of spam at commit event for some obscure reason. I couldn't fix it fast, so reverting.

Original issue's description:
> Made _discard_pending() always post a message. Added meaningful
> default messages to all the places where it is called in the code.  In
> particular, CQ will now always post a message whenever the Commit
> checkbox is unchecked, for any reason.
> 
> Updated unit tests accordingly, and made them a bit more robust by
> adding an error message to the failing FakeVerifier.
> 
> This does NOT fix the bug, but will hopefully give more visibility to
> developers when a CL is dropped.
> 
> BUG=238283
> 
> Committed: http://src.chromium.org/viewvc/chrome?view=rev&revision=247488

TBR=phajdan.jr@chromium.org
NOTREECHECKS=true
NOTRY=true
BUG=238283
Committed: http://src.chromium.org/viewvc/chrome?view=rev&revision=248624

[Sergey Berezin, 2014-02-04 00:06:05]

Created Revert of CQ to always post a message when Commit box is unchecked.

[commit-bot: I haz the power, 2014-02-04 00:06:08]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2014-02-04 00:06:09]

No LGTM from a valid reviewer yet. Only full committers are accepted.
Even if an LGTM may have been provided, it was from a non-committer or
a lowly provisional committer, _not_ a full super star committer.
See http://www.chromium.org/getting-involved/become-a-committer
Note that this has nothing to do with OWNERS files.

[commit-bot: I haz the power, 2014-02-04 00:06:17]

CQ bit was unchecked on CL. Ignoring.

[Paweł Hajdan Jr., 2014-02-04 00:08:37]

LGTM

[Sergey Berezin, 2014-02-04 00:10:12]

The CQ bit was checked by sergeyberezin@chromium.org

[commit-bot: I haz the power, 2014-02-04 00:10:14]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/sergeyberezin@chromium.org/138133014/1

[commit-bot: I haz the power, 2014-02-04 00:10:46]

Change committed as 248624

[commit-bot: I haz the power, 2014-02-04 00:10:50]

CQ bit was unchecked on CL. Ignoring.

[commit-bot: I haz the power, 2014-02-04 00:10:51]

CQ bit was unchecked on CL. Ignoring.

[commit-bot: I haz the power, 2014-02-04 00:10:52]

CQ bit was unchecked on CL. Ignoring.

[commit-bot: I haz the power, 2014-02-04 00:10:53]

CQ bit was unchecked on CL. Ignoring.

[commit-bot: I haz the power, 2014-02-04 00:14:24]

CQ bit was unchecked on CL. Ignoring.