Add underscore to make featureFlags optional

Author: AllanGuigou

languageservice/src/complete.ts

@@ -532,7 +532,7 @@ function getExpressionCompletionItems(
   context: DescriptionDictionary,
   extensionFunctions: FunctionInfo[],
   pos: Position,
-  featureFlags?: FeatureFlags
+  _featureFlags?: FeatureFlags
 ): CompletionItem[] {
   if (!token.range) {
     return [];