fix custom_elements_test on ie10
fix custom_elements_test on ie10

Pete warned me about this one test that isn't using the loadPolyfill function, but I forgot to fix it in last change.

by deleting the custom copy, it will pick up the one in utils, and that one correctly loads MutationObserver polyfill

Review URL: https://codereview.chromium.org//133053005

git-svn-id: c93d8a2297af3b929165606efe145742a534bc71@32176 260f80e4-7a28-3924-810f-c04153c831b5

dartino/dart-sdk,dart-archive/dart-sdk,dartino/dart-sdk,dartino/dart-sdk,dartino/dart-sdk,dart-archive/dart-sdk,dart-archive/dart-sdk,dart-lang/sdk,dart-archive/dart-sdk,dartino/dart-sdk,dart-archive/dart-sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-archive/dart-sdk,dartino/dart-sdk,dart-archive/dart-sdk,dartino/dart-sdk,dart-lang/sdk,dart-lang/sdk,dartino/dart-sdk,dart-archive/dart-sdk,dartino/dart-sdk,dart-lang/sdk,dart-archive/dart-sdk,dart-lang/sdk