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

sky/tests/mutation-observer/transient-gc-crash.sky

Index: sky/tests/mutation-observer/transient-gc-crash.sky
diff --git a/sky/tests/mutation-observer/transient-gc-crash.sky b/sky/tests/mutation-observer/transient-gc-crash.sky
deleted file mode 100644
index e6d4bb6af4e18efc64200a7a4b1161732d1e57f0..0000000000000000000000000000000000000000
--- a/sky/tests/mutation-observer/transient-gc-crash.sky
+++ /dev/null
@@ -1,22 +0,0 @@
-<script src="../../../resources/js-test.js"></script>
-<script>
-window.jsTestIsAsync = true;
-description('Clearing transient observers after observation node is GCed should not cause a crash.');
-
-function callback(mutations) {
-    window.mutations = mutations;
-}
-var observer = new MutationObserver(callback);
-
-var div = document.createElement('div');
-var span = div.appendChild(document.createElement('span'));
-observer.observe(div, {attributes: true, subtree: true});
-div.removeChild(span);
-div = null;
-gc();
-span.setAttribute('foo', 'bar');
-setTimeout(function() {
-    shouldBe('mutations.length', '1');
-    finishJSTest();
-}, 0);
-</script>