Revert "fix: 添加 GenerationRecord.updated_at 字段（修复 Celery 僵尸任务恢复报错）"

This reverts commit 81f9cc923a9c6458f7ac49dd382a7d32ab404ef8.

backend/apps/generation/migrations/0014_add_updated_at.py

@@ -1,18 +0,0 @@
-# Generated by Django 4.2.29 on 2026-03-28 19:32
-
-from django.db import migrations, models
-
-
-class Migration(migrations.Migration):
-
-    dependencies = [
-        ('generation', '0013_add_video_token_price'),
-    ]
-
-    operations = [
-        migrations.AddField(
-            model_name='generationrecord',
-            name='updated_at',
-            field=models.DateTimeField(auto_now=True, verbose_name='更新时间'),
-        ),
-    ]