Remove a nonexistent file from BUILD.gn to fix Mac GN Build failure

Remove a nonexistent file from BUILD.gn to fix Mac GN Build failure

http://build.chromium.org/p/chromium.mac/builders/Mac%20GN/builds/11962

BUG=474828
TBR=shuchen@chromium.org,sky@chromium.org
NOTRY=true

Committed: https://crrev.com/2091a8ed54fe3609bfe4f88fedeff53f6a3e3020
Cr-Commit-Position: refs/heads/master@{#337166}

[nhiroki, 2015-07-02 03:13:20]

nhiroki@chromium.org changed reviewers:
+ shuchen@chromium.org

[nhiroki, 2015-07-02 03:17:28]

nhiroki@chromium.org changed reviewers:
+ sky@chromium.org

[nhiroki, 2015-07-02 03:18:12]

The CQ bit was checked by nhiroki@chromium.org

[nhiroki, 2015-07-02 03:18:24]

The CQ bit was unchecked by nhiroki@chromium.org

[nhiroki, 2015-07-02 03:19:17]

The CQ bit was checked by nhiroki@chromium.org

[commit-bot: I haz the power, 2015-07-02 03:19:21]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1217783003/1

[commit-bot: I haz the power, 2015-07-02 03:25:13]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-07-02 03:26:11]

Patchset 1 (id:??) landed as
https://crrev.com/2091a8ed54fe3609bfe4f88fedeff53f6a3e3020
Cr-Commit-Position: refs/heads/master@{#337166}

[Shu Chen, 2015-07-02 03:30:50]

lgtm