Remove Sky tests that we don't intend to port to the new world

sky/tests/layout/custom-dirty-bits.sky

Index: sky/tests/layout/custom-dirty-bits.sky
diff --git a/sky/tests/layout/custom-dirty-bits.sky b/sky/tests/layout/custom-dirty-bits.sky
deleted file mode 100644
index d8ecf25085cc268e1186cf143fb503867b7b47a0..0000000000000000000000000000000000000000
--- a/sky/tests/layout/custom-dirty-bits.sky
+++ /dev/null
@@ -1,16 +0,0 @@
-<import src="../resources/dump-as-render-tree.sky" />
-
-<block>hello</block>
-
-<script>
-import 'dart:sky';
-
-void main() {
-  // This tests custom layout of text nodes inside non-paragraphs.
-  // They shouldn't show up in the render tree at all, so they
-  // don't need laying out.
-  // This test passes if it doesn't crash and the render tree
-  // has no RenderTexts.
-  document.querySelector('block').setLayoutManager(() {}, () {});
-}
-</script>