Revert "Add output reference to gen written files."

Revert "Add output reference to gen written files."

This reverts commit c497d21798caf871326443ad98bd58f546d7b38e.
AKA https://codereview.chromium.org/1252403005/

TBR=dpranke@chromium.org
BUG=533067
TEST=local re-run of gn gen in a few scenarios

Committed: https://crrev.com/a4a5e48c471822d1c51dd00233bf3a167e00d80e
Cr-Commit-Position: refs/heads/master@{#351319}

[Peter Mayo, 2015-09-29 14:55:24]

The CQ bit was checked by petermayo@chromium.org

[commit-bot: I haz the power, 2015-09-29 14:55:41]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1381443002/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1381443002/1

[commit-bot: I haz the power, 2015-09-29 15:09:34]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-09-29 15:10:23]

Patchset 1 (id:??) landed as
https://crrev.com/a4a5e48c471822d1c51dd00233bf3a167e00d80e
Cr-Commit-Position: refs/heads/master@{#351319}

[Dirk Pranke, 2015-09-29 17:03:15]

lgtm