Revert of Enable gbm platform by default in ozone builds

Revert of Enable gbm platform by default in ozone builds (patchset #2 id:20001 of https://codereview.chromium.org/1336023002/ )

Reason for revert:
Broke chrome-sdk builds until it updates.


Original issue's description:
> Enable gbm platform by default in ozone builds
> 
> Now that we have minigbm in third_party we can set ozone_platform_gbm=1 by default.
> 
> BUG=530712
> TEST=tryjobs for linux_chromium_chromeos_ozone_rel_ng,
>   cast_shell_linux
> 
> Committed: https://crrev.com/88e504e383e7641e139bc836b33ded00a0d46668
> Cr-Commit-Position: refs/heads/master@{#348802}

TBR=dpranke@chromium.org
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=530712

[spang, 2015-09-15 23:46:24]

Created Revert of Enable gbm platform by default in ozone builds

[Dirk Pranke, 2015-09-15 23:50:34]

lgtm

[spang, 2015-09-15 23:56:02]

The CQ bit was unchecked by spang@chromium.org

[spang, 2015-09-15 23:56:02]

The CQ bit was checked by spang@chromium.org

[commit-bot: I haz the power, 2015-09-16 00:05:53]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1342323002/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1342323002/1

[spang, 2015-09-16 00:06:13]

The CQ bit was unchecked by spang@chromium.org

[spang, 2015-09-16 00:06:16]

The CQ bit was checked by spang@chromium.org

[commit-bot: I haz the power, 2015-09-16 00:07:43]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1342323002/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1342323002/1

[spang, 2015-09-16 00:10:31]

The CQ bit was unchecked by spang@chromium.org

[commit-bot: I haz the power, 2015-09-16 00:11:29]

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