Remove dart backend

test/dart_codegen/expect/types.txt

Index: test/dart_codegen/expect/types.txt
diff --git a/test/dart_codegen/expect/types.txt b/test/dart_codegen/expect/types.txt
deleted file mode 100644
index 7ff2d08afa8232f9f31a659e4443e584cd6ddeef..0000000000000000000000000000000000000000
--- a/test/dart_codegen/expect/types.txt
+++ /dev/null
@@ -1,13 +0,0 @@
-// Messages from compiling types.dart
-info: line 10, column 6 of test/dart_codegen/types/c.dart: [DynamicCast] f4(3) (dynamic) will need runtime check to cast to type A
-  f3(f4(3));
-     ^^^^^
-warning: line 11, column 6 of test/dart_codegen/types/c.dart: [DownCastComposite] f4 ((dynamic) → dynamic) will need runtime check to cast to type (A) → A
-  f1(f4);
-     ^^
-info: line 10, column 14 of test/dart_codegen/types/d.dart: [DynamicCast] f4("""hello""") (dynamic) will need runtime check to cast to type A
-  var x = f3(f4("""hello"""));
-             ^^^^^^^^^^^^^^^
-warning: line 11, column 14 of test/dart_codegen/types/d.dart: [DownCastComposite] f4 ((dynamic) → dynamic) will need runtime check to cast to type (A) → A
-  var y = f1(f4);
-             ^^