Revert "Flatten futures when inferring the type of an async function expression."

pkg/front_end/testcases/inference/async_closure_return_type_flatten.dart.strong.expect

Index: pkg/front_end/testcases/inference/async_closure_return_type_flatten.dart.strong.expect
diff --git a/pkg/front_end/testcases/inference/async_closure_return_type_flatten.dart.strong.expect b/pkg/front_end/testcases/inference/async_closure_return_type_flatten.dart.strong.expect
deleted file mode 100644
index 68d859c9fcc9003db69f25f0c6b192d919eea6ef..0000000000000000000000000000000000000000
--- a/pkg/front_end/testcases/inference/async_closure_return_type_flatten.dart.strong.expect
+++ /dev/null
@@ -1,36 +0,0 @@
-library test;
-import self as self;
-import "dart:async" as asy;
-import "dart:core" as core;
-
-static field asy::Future<core::int> futureInt = null;
-static field () → asy::Future<core::int> f = () → dynamic => self::futureInt;
-static field () → asy::Future<core::int> g = () → dynamic /* originally async */ {
-  final asy::Completer<asy::FutureOr<dynamic>> :completer = asy::Completer::sync<asy::FutureOr<dynamic>>();
-  asy::FutureOr<dynamic> :return_value;
-  dynamic :async_op_then;
-  dynamic :async_op_error;
-  dynamic :await_jump_var = 0;
-  dynamic :await_ctx_var;
-  function :async_op([dynamic :result, dynamic :exception, dynamic :stack_trace]) → dynamic yielding 
-    try {
-      #L1:
-      {
-        :return_value = self::futureInt;
-        break #L1;
-      }
-      :completer.complete(:return_value);
-      return;
-    }
-    on dynamic catch(dynamic :exception, dynamic :stack_trace) {
-      :completer.completeError(:exception, :stack_trace);
-    }
-  :async_op_then = asy::_asyncThenWrapperHelper(:async_op);
-  :async_op_error = asy::_asyncErrorWrapperHelper(:async_op);
-  asy::Future::microtask<dynamic>(:async_op);
-  return :completer.future;
-};
-static method main() → dynamic {
-  self::f;
-  self::g;
-}