Don't pull in mojo on iOS.

This ended up pulling in a bunch of v8 code that doesn't work with the
ninja-xcode bindings.

BUG=

Review URL: https://codereview.chromium.org/1922863003

Cr-Commit-Position: refs/heads/master@{#389888}

url/url.gyp

@@ -74,7 +74,6 @@
       'type': 'executable',
       'dependencies': [
         '../base/base.gyp:test_support_base',
-        '../mojo/mojo_edk.gyp:mojo_common_test_support',
         '../testing/gtest.gyp:gtest',
         '../third_party/icu/icu.gyp:icuuc',
         'url_test_mojom',
@@ -96,6 +95,9 @@
           'sources': [
             'mojo/url_gurl_struct_traits_unittest.cc',
           ],
+          'dependencies': [
+            '../mojo/mojo_edk.gyp:mojo_common_test_support',
+          ],
         }],
         # Unit tests that are not supported by the current ICU alternatives on Android.
         ['OS == "android" and use_platform_icu_alternatives == 1', {