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

sky/tests/mutation-observer/observe-subtree-expected.txt

Index: sky/tests/mutation-observer/observe-subtree-expected.txt
diff --git a/sky/tests/mutation-observer/observe-subtree-expected.txt b/sky/tests/mutation-observer/observe-subtree-expected.txt
deleted file mode 100644
index 9ae9a7faa622cd864337d39887fe2610f7f650ce..0000000000000000000000000000000000000000
--- a/sky/tests/mutation-observer/observe-subtree-expected.txt
+++ /dev/null
@@ -1,9 +0,0 @@
-Running 5 tests
-ok 1 MutationObserver.observe on a subtree should handle basic aspects of subtree observation
-ok 2 MutationObserver.observe on a subtree should handle two observers at different depths
-ok 3 MutationObserver.observe on a subtree should handle one observer at two different depths
-ok 4 MutationObserver.observe on a subtree should handle transiently detached nodes are still observed via subtree
-ok 5 MutationObserver.observe on a subtree should have correct behavior of transient observation with complex movement
-5 tests
-5 pass
-0 fail