Remove stale dependency in "ozone_demo" GN target.

Remove stale dependency in "ozone_demo" GN target.

The target "ui/ozone/gpu" no longer exists. Remove the dependency on it.
Also remove reference to this directory in content/DEPS.

To test, set use_ozone=true in gn args and perform a build of
ui/ozone/demo:ozone_demo.

BUG=

Committed: https://crrev.com/07ea627e1310ea81313db708d044753e7507b100
Cr-Commit-Position: refs/heads/master@{#341783}

[slan, 2015-08-04 17:00:22]

slan@chromium.org changed reviewers:
+ jam@chromium.org, spang@chromium.org

[slan, 2015-08-04 17:00:22]

Encountered this issue while building Chromecast with GN. PTAL.

[spang, 2015-08-04 17:00:59]

lgtm

[slan, 2015-08-04 17:02:37]

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

[commit-bot: I haz the power, 2015-08-04 17:04:13]

Dry run: CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1262623009/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1262623009/1

[slan, 2015-08-04 17:45:48]

slan@chromium.org changed reviewers:
+ nasko@chromium.org

[slan, 2015-08-04 17:45:49]

+nasko for content/DEPS

[commit-bot: I haz the power, 2015-08-04 17:52:16]

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

[commit-bot: I haz the power, 2015-08-04 17:52:17]

Dry run: This issue passed the CQ dry run.

[jam, 2015-08-04 20:15:27]

lgtm

[slan, 2015-08-04 20:28:27]

The CQ bit was checked by slan@chromium.org

[commit-bot: I haz the power, 2015-08-04 20:28:53]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1262623009/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1262623009/1

[commit-bot: I haz the power, 2015-08-04 20:37:48]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-08-04 20:39:12]

Patchset 1 (id:??) landed as
https://crrev.com/07ea627e1310ea81313db708d044753e7507b100
Cr-Commit-Position: refs/heads/master@{#341783}