Move kernel baseline tests to front_end.

pkg/kernel/testcases/strong-mode/async_function.baseline.txt

Index: pkg/kernel/testcases/strong-mode/async_function.baseline.txt
diff --git a/pkg/kernel/testcases/strong-mode/async_function.baseline.txt b/pkg/kernel/testcases/strong-mode/async_function.baseline.txt
deleted file mode 100644
index d498bf6fbfea9a980bf598824b861c3ae872074c..0000000000000000000000000000000000000000
--- a/pkg/kernel/testcases/strong-mode/async_function.baseline.txt
+++ /dev/null
@@ -1,11 +0,0 @@
-library;
-import self as self;
-import "dart:async" as asy;
-import "dart:core" as core;
-
-static method asyncString() → asy::Future<core::String> async {
-  return "foo";
-}
-static method main() → dynamic async {
-  core::String str = await self::asyncString();
-}