Remove usage of TypeSwitch.

src/Features/CSharp/Portable/ExtractMethod/CSharpSelectionValidator.cs

@@ -431,7 +431,8 @@ public override IEnumerable<SyntaxNode> GetOuterReturnStatements(SyntaxNode comm
             }
 
             // make sure this method doesn't have return type.
-            return method.ReturnType.TypeSwitch((PredefinedTypeSyntax p) => p.Keyword.Kind() == SyntaxKind.VoidKeyword);
+            return method.ReturnType is PredefinedTypeSyntax p &&
+                p.Keyword.Kind() == SyntaxKind.VoidKeyword;
         }
 
         private static TextSpan GetAdjustedSpan(SourceText text, TextSpan textSpan)