Improve test and comments

Test asserts that unused locals error works for untyped modules.
Comment no longer claims to check for untyped modules.

src/compiler/utilities.ts

@@ -438,7 +438,7 @@ namespace ts {
             ((<ModuleDeclaration>node).name.kind === SyntaxKind.StringLiteral || isGlobalScopeAugmentation(<ModuleDeclaration>node));
     }
 
-    /** Given a symbol for a module, checks that it is either an untyped import or a shorthand ambient module. */
+    /** Given a symbol for a module, checks that it is a shorthand ambient module. */
     export function isShorthandAmbientModuleSymbol(moduleSymbol: Symbol): boolean {
         return isShorthandAmbientModule(moduleSymbol.valueDeclaration);
     }