在庫一覧の関数の重複定義を修正

frontend/src/pages/StockPage.tsx

@@ -39,14 +39,6 @@ const formatDateLocal = (date: Date) => {
   return `${year}-${month}-${day}`;
 };
 
-// 日付をyyyy-MM-dd形式で返す関数
-const formatDateLocal = (date: Date) => {
-  const year = date.getFullYear();
-  const month = (date.getMonth() + 1).toString().padStart(2, '0');
-  const day = date.getDate().toString().padStart(2, '0');
-  return `${year}-${month}-${day}`;
-};
-
 // 新規在庫の初期状態
 const EMPTY_STOCK: Omit<Stock, 'stockId' | 'stuffId'> & { stuffId: number | null } & { newAddition: boolean } = {
   stuffId: null,