修复前端构建错误：移除未使用的图标导入

移除 ExamManagement.tsx 中未使用的图标：
- ClockCircleOutlined
- CheckCircleOutlined

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

web/src/pages/ExamManagement.tsx

@@ -23,8 +23,6 @@ import {
   DeleteOutlined,
   PlayCircleOutlined,
   FileTextOutlined,
-  ClockCircleOutlined,
-  CheckCircleOutlined,
   TrophyOutlined,
   HistoryOutlined,
   PrinterOutlined,