Delete Sky tests that we're not going to run with Dart

Delete Sky tests that we're not going to run with Dart

This CL removes a number of tests that we don't plan to port to Dart:

1) custom-elements. We're going to use a different mechanism for custom
   elements. We'll need to write a new set of tests as we implement it.
2) inspector. These are tests of the JS inspector backend, which we don't
   plan to use.
3) js. This is a test of a JavaScript feature.
4) mocha. These are tests of the JavaScript testing framework we were using.
5) mutation-observer. We're keeping the C++ code for mutation observers, but
   it's unclear how we want to expose this in the platform.
6) resources. These are JavaScript-based testing frameworks.

R=eseidel@chromium.org, ojan@chromium.org

Committed: https://chromium.googlesource.com/external/mojo/+/f30411abfd4abee7da7350f86e872606dd1bd08e

[eseidel, 2015-02-13 18:38:35]

eseidel@chromium.org changed reviewers:
+ eseidel@chromium.org

[eseidel, 2015-02-13 18:38:36]

lgtm

[ojan, 2015-02-13 18:55:17]

lgtm

[abarth-chromium, 2015-02-13 21:51:31]

Committed patchset #1 (id:1) manually as
f30411abfd4abee7da7350f86e872606dd1bd08e (presubmit successful).