移除 CashDiscountGrant 中未使用的 randomDate 函数

修复 ESLint no-unused-vars 报错。发放时间改用 randomDateTime 派生后，原 randomDate 已无引用。

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

pc/src/views/CashDiscountGrant.vue

@@ -104,12 +104,6 @@ const GRANT_REASONS = ['新开户礼遇', '月度消费达标奖励', '生日专
 
 function pad(n) { return String(n).padStart(2, '0') }
 
-function randomDate(baseDate, offsetDays) {
-  const d = new Date(baseDate)
-  d.setDate(d.getDate() - Math.floor(Math.random() * offsetDays))
-  return `${d.getFullYear()}-${pad(d.getMonth() + 1)}-${pad(d.getDate())}`
-}
-
 function randomDateTime(baseDate, offsetDays) {
   const d = new Date(baseDate)
   d.setDate(d.getDate() - Math.floor(Math.random() * offsetDays))