Remove an unnecessary type annotation and an unnecessary await

Change-Id: Idbd451680592e3eb1ac9cc1c13ef2e13e1855057
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/159320
Reviewed-by: Konstantin Shcheglov <scheglov@google.com>
Commit-Queue: Brian Wilkerson <brianwilkerson@google.com>

pkg/analysis_server/lib/src/services/refactoring/extract_method.dart

@@ -718,7 +718,7 @@ class ExtractMethodRefactoringImpl extends RefactoringImpl
     }
     // maybe ends with "return" statement
     if (_selectionStatements != null) {
-      TypeSystem typeSystem = await resolveResult.typeSystem;
+      var typeSystem = resolveResult.typeSystem;
       var returnTypeComputer = _ReturnTypeComputer(typeSystem);
       _selectionStatements.forEach((statement) {
         statement.accept(returnTypeComputer);