Remove redundant OS checks in chrome_shell.gypi

Remove redundant OS checks in chrome_shell.gypi

chrome_shell.gypi is only included if OS=="android" so there is no reason
to test it again.

BUG=none

Committed: https://crrev.com/8c70705f1cb3d9726c3ba8f782209173193f8d3e
Cr-Commit-Position: refs/heads/master@{#311517}

[mstrum, 2015-01-13 16:47:24]

mstrum@amazon.com changed reviewers:
+ newt@chromium.org

[mstrum, 2015-01-13 16:47:25]

mstrum@amazon.com changed required reviewers:
+ newt@chromium.org

[mstrum, 2015-01-13 16:50:00]

Hi newt,

PTAL, I noticed these so I thought I'd clean it up a little~

- Matt

[newt (away), 2015-01-14 16:40:30]

lgtm

[mstrum, 2015-01-14 16:47:20]

The CQ bit was checked by mstrum@amazon.com

[commit-bot: I haz the power, 2015-01-14 16:47:41]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/810193006/1

[commit-bot: I haz the power, 2015-01-14 18:24:42]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-01-14 18:25:39]

Patchset 1 (id:??) landed as
https://crrev.com/8c70705f1cb3d9726c3ba8f782209173193f8d3e
Cr-Commit-Position: refs/heads/master@{#311517}