Remove GN group backward-compat code.

Remove GN group backward-compat code.

This backwards-compat code automatically promoted a group's deps to be public if there were no public deps defined. This was done to make the transition to adding public/private deps easier.

Dependent on:
https://codereview.chromium.org/1356493004/ (chrome)
https://codereview.chromium.org/1351203002/ (blink)
https://codereview.chromium.org/1356723002/ (v8)

Committed: https://crrev.com/2616020c823cbf4cba3f1ad05f042952b8bacb05
Cr-Commit-Position: refs/heads/master@{#352071}

[brettw, 2015-09-17 22:29:50]

brettw@chromium.org changed reviewers:
+ dpranke@chromium.org

[Dirk Pranke, 2015-09-17 23:12:43]

lgtm

[brettw, 2015-10-02 17:33:22]

The CQ bit was checked by brettw@chromium.org

[commit-bot: I haz the power, 2015-10-02 17:35:03]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1353023004/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1353023004/1

[commit-bot: I haz the power, 2015-10-02 17:53:34]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-10-02 17:54:11]

Patchset 1 (id:??) landed as
https://crrev.com/2616020c823cbf4cba3f1ad05f042952b8bacb05
Cr-Commit-Position: refs/heads/master@{#352071}