Add maruel, remove cmp&darin from //testing/buildbot/OWNERS.

Add maruel, remove cmp&darin from //testing/buildbot/OWNERS.

As part of issues 496321 and 98637, I'll start sending a fair number of
(somewhat) mechanical changes.

cmp and darin are not coding on the chromium project anymore.

R=jam@chromium.org
BUG=

Committed: https://crrev.com/4f2ff6852e6838ea671e0d2322a57b1c51b22948
Cr-Commit-Position: refs/heads/master@{#332993}

[jam, 2015-06-04 21:35:52]

lgtm

[M-A Ruel, 2015-06-04 21:45:00]

The CQ bit was checked by maruel@chromium.org

[commit-bot: I haz the power, 2015-06-04 21:46:13]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1157673005/1

[commit-bot: I haz the power, 2015-06-04 22:05:09]

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

[commit-bot: I haz the power, 2015-06-04 22:05:10]

Try jobs failed on following builders:
  android_chromium_gn_compile_rel on tryserver.chromium.linux (JOB_FAILED,
http://build.chromium.org/p/tryserver.chromium.linux/builders/android_chromiu...)

[M-A Ruel, 2015-06-05 01:44:51]

The CQ bit was checked by maruel@chromium.org

[commit-bot: I haz the power, 2015-06-05 01:45:14]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1157673005/1

[commit-bot: I haz the power, 2015-06-05 02:13:10]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-06-05 02:13:56]

Patchset 1 (id:??) landed as
https://crrev.com/4f2ff6852e6838ea671e0d2322a57b1c51b22948
Cr-Commit-Position: refs/heads/master@{#332993}