Build aura_shell_unittests on Mac try bot target

Enables building of target 'aura_shell_unittest' when building the
'aura_builder' target.  The 'aura_builder' target is used by the try
bots.

BUG=None
TEST=Compiles on Mac try bot
R=oshima@chromium.org

Review URL: https://chromiumcodereview.appspot.com/9317097

git-svn-id: http://src.chromium.org/svn/trunk/src/build@120453 4ff67af0-8c30-449e-8e8b-ad334ec8d88c

all.gyp

@@ -611,7 +611,6 @@
             ['OS=="mac"', {
               # Exclude dependencies that are not currently implemented.
               'dependencies!': [
-                '../ash/ash.gyp:aura_shell_unittests',
                 '../chrome/chrome.gyp:chrome',
                 '../chrome/chrome.gyp:unit_tests',
                 '../chrome/chrome.gyp:ui_tests',