Remove chromium_builder_asan_mac target from all.gyp

It was just an alias for chromium_builder_asan and it was removed from
the buildbot scripts at https://codereview.chromium.org/257903004 (
svn://svn.chromium.org/chrome/trunk/tools/build@266374)

BUG=None
TEST=green trybots
R=dpranke@chromium.org
NOTRY=true

Review URL: https://codereview.chromium.org/270623002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@269652 0039d316-1c4b-4281-b951-d872f2087c98

build/all.gyp

@@ -930,14 +930,6 @@
             '../url/url.gyp:url_unittests',
           ],
         },
-        {
-          # TODO(dpranke): Update the bots to refer to 'chromium_builder_asan'.
-          'target_name': 'chromium_builder_asan_mac',
-          'type': 'none',
-          'dependencies': [
-            'chromium_builder_asan'
-          ],
-        },
         {
           'target_name': 'chromium_builder_dbg_valgrind_mac',
           'type': 'none',