[turbofan] Remove hack for dead nodes from JSGenericLowering.

[turbofan] Remove hack for dead nodes from JSGenericLowering.

Now that the graph is being trimmed after generic lowering, we can drop
this workaround. The diamond will no longer confuse the scheduler.

R=bmeurer@chromium.org

Committed: https://crrev.com/25e687965fdc380b722712b45716ce1a6db79e3b
Cr-Commit-Position: refs/heads/master@{#29081}

[Benedikt Meurer, 2015-06-17 11:11:55]

The CQ bit was checked by bmeurer@chromium.org

[Benedikt Meurer, 2015-06-17 11:11:56]

lgtm

[commit-bot: I haz the power, 2015-06-17 11:12:05]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1191913002/1

[commit-bot: I haz the power, 2015-06-17 11:29:57]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-06-17 11:30:13]

Patchset 1 (id:??) landed as
https://crrev.com/25e687965fdc380b722712b45716ce1a6db79e3b
Cr-Commit-Position: refs/heads/master@{#29081}