Run tree shaking in strong-mode baseline tests.

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

 library;
 import self as self;
 import "dart:async" as asy;
 import "dart:core" as core;
 
-static field core::List<core::String> stringList = <core::String>["bar"];
 static method asyncString() → asy::Future<core::String> async {
   return "foo";
 }
-static method asyncString2() → asy::Future<core::String> async {
-  return self::asyncString();
-}
-static method syncStarString() → core::Iterable<core::String> sync* {
-  yield "foo";
-  yield* self::syncStarString2();
-  yield* self::stringList;
-}
-static method syncStarString2() → core::Iterable<core::String> sync* {
-  yield "foo";
-}
-static method asyncStarString() → asy::Stream<core::String> async* {
-  yield "foo";
-  yield* self::asyncStarString2();
-  yield await self::asyncString();
-}
-static method asyncStarString2() → asy::Stream<core::String> async* {
-  yield "bar";
-}
 static method main() → dynamic async {
   core::String str = await self::asyncString();
 }