Remove build/module_args/dart.gni

Remove build/module_args/dart.gni

Now that we're no longer rolling mojo into chrome,
we no longer need to worry about keeping around a
reference to an empty dart.gni file.

R=rockot@chromium.org
BUG=

Committed: https://crrev.com/71a32a6f3f77e5ceb2022087ad7b1aea726fcbf2
Cr-Commit-Position: refs/heads/master@{#353466}

[Dirk Pranke, 2015-10-09 22:23:37]

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

[commit-bot: I haz the power, 2015-10-09 22:25:08]

Dry run: CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1395013003/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1395013003/1

[Ken Rockot(use gerrit already), 2015-10-09 22:25:21]

lgtm

[commit-bot: I haz the power, 2015-10-10 00:21:04]

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

[commit-bot: I haz the power, 2015-10-10 00:21:05]

Dry run: This issue passed the CQ dry run.

[Dirk Pranke, 2015-10-10 18:31:52]

The CQ bit was checked by dpranke@chromium.org

[commit-bot: I haz the power, 2015-10-10 18:32:19]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1395013003/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1395013003/1

[commit-bot: I haz the power, 2015-10-10 18:38:47]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-10-10 18:39:45]

Patchset 1 (id:??) landed as
https://crrev.com/71a32a6f3f77e5ceb2022087ad7b1aea726fcbf2
Cr-Commit-Position: refs/heads/master@{#353466}