Revert 222971 "Switch all windows bots to Aura"

> Switch all windows bots to Aura
> 
> This is a reland of https://codereview.chromium.org/23816007/
> See the comments there.
> 
> Hopefully all pesky tests failures have been addressed
> 
> BUG=259185
> TEST=none
> TBR=scottmg
> 
> Review URL: https://codereview.chromium.org/23803010

TBR=cpu@chromium.org

Review URL: https://codereview.chromium.org/23796008

git-svn-id: http://src.chromium.org/svn/trunk/src/build@222983 4ff67af0-8c30-449e-8e8b-ad334ec8d88c

common.gypi

@@ -69,15 +69,10 @@
           'branding%': 'Chromium',
 
           'conditions': [
-            # ChromeOS implies ash and Windows implies Ash and Aura.
-            # However, we only default use_ash to 1 on Windows if
-            # use_aura==1, so that disabling Aura automatically
-            # disables Ash. See comments below, as well.
-            ['chromeos==1 or OS=="win"', {
-              'use_aura%': 1,
-            }],
+            # ChromeOS implies ash.
             ['chromeos==1', {
               'use_ash%': 1,
+              'use_aura%': 1,
             }],
 
             # For now, Windows builds that |use_aura| should also imply using