[ozone] Remove unneeded workaround for disabling display controllers.

[ozone] Remove unneeded workaround for disabling display controllers.

In the past due to a kernel error, modesetting with a null fb didn't
release the front buffer, this workaround was put in place. Kernel bug was
fixed and this is no longer needed.

BUG=

Committed: https://crrev.com/b3c13d3f1417dd484834940b3e749c97cafdc7c7
Cr-Commit-Position: refs/heads/master@{#330196}

[alexst (slow to review), 2015-05-15 19:40:54]

alexst@chromium.org changed reviewers:
+ dnicoara@chromium.org

[dnicoara, 2015-05-15 20:14:57]

lgtm

[dnicoara, 2015-05-15 20:15:03]

The CQ bit was checked by dnicoara@chromium.org to run a CQ dry run

[commit-bot: I haz the power, 2015-05-15 20:16:49]

Dry run: CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1130613003/1

[commit-bot: I haz the power, 2015-05-15 20:51:43]

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

[commit-bot: I haz the power, 2015-05-15 20:51:44]

Dry run: This issue passed the CQ dry run.

[dnicoara, 2015-05-15 20:56:56]

The CQ bit was checked by dnicoara@chromium.org

[commit-bot: I haz the power, 2015-05-15 20:58:42]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1130613003/1

[commit-bot: I haz the power, 2015-05-15 21:08:23]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-05-18 11:27:30]

Patchset 1 (id:??) landed as
https://crrev.com/b3c13d3f1417dd484834940b3e749c97cafdc7c7
Cr-Commit-Position: refs/heads/master@{#330196}