cc: remove useless forward_begin_frames_to_children flags in SchedulerSettings

cc: remove useless forward_begin_frames_to_children flags in SchedulerSettings

This flag is not used.
Instead, SetChildrenNeedBeginFrames() will be used to control child compositor's
frame scheduling.

R=brianderson@chromium.org
BUG=467416
TEST=cc_unittests

Committed: https://crrev.com/ddd3ce180015e8f3ec7509af1d5566778a10ca6d
Cr-Commit-Position: refs/heads/master@{#320734}

[simonhong, 2015-03-15 22:47:49]

PTAL.

[brianderson, 2015-03-16 15:32:03]

lgtm

[simonhong, 2015-03-16 15:36:44]

The CQ bit was checked by simonhong@chromium.org

[commit-bot: I haz the power, 2015-03-16 15:36:51]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1010623002/1

[commit-bot: I haz the power, 2015-03-16 16:17:53]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-03-16 16:18:46]

Patchset 1 (id:??) landed as
https://crrev.com/ddd3ce180015e8f3ec7509af1d5566778a10ca6d
Cr-Commit-Position: refs/heads/master@{#320734}