Revert 221936 "Switch all windows bots to use Aura."

breaks XP Tests:
ActivityLogPrerenderTest.TestScriptInjected
FindInPageTest.PrepopulateRespectBlank
KeyboardAccessTest.TestAltMenuKeyboardAccessFocusOmnibox
KeyboardAccessTest.TestMenuKeyboardOpenDismiss

> Switch all windows bots to use Aura.
> 
> Because we've been shipping Aura to canary for a while. And because force compositor landed 40 hours ago and things seem ok. See https://codereview.chromium.org/23874016/
> 
> This also allows to see perf numbers for Aura. 
> 
> This has happened before see for example r204698, r211007 and 214056 as an experiment but this time it might stick.
> 
> BUG=259185
> TEST=none
> TBR=scottmg
> 
> Review URL: https://codereview.chromium.org/23816007

TBR=cpu@chromium.org

Review URL: https://codereview.chromium.org/23523035

git-svn-id: http://src.chromium.org/svn/trunk/src/build@221952 4ff67af0-8c30-449e-8e8b-ad334ec8d88c

common.gypi

@@ -69,8 +69,8 @@
           'branding%': 'Chromium',
 
           'conditions': [
-            # ChromeOS implies ash and Windows implies Ash and Aura.
-            ['chromeos==1 or OS=="win"', {
+            # ChromeOS implies ash.
+            ['chromeos==1', {
               'use_ash%': 1,
               'use_aura%': 1,
             }],