Revert "Migrate backup sync controller from code-generator to kubebui…

[blackpiglet]

…lder (#4423)"

This reverts commit 5aaeb3e.

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This commit is used to revert #4423.
After #4423 is merged, we found backup sync controller is not expected to work as a list-watch way. Before refactor, backup sync controller actually works as an time-routine job, which is implemented by velero generic controller as an goroutine sleeps by the resyncPeriod then runs the resyncFunc.
The refactor code uses Reconcile to watch Backup CR as event trigger to backup sync.
Actually, the backup sync task should work, but the sync process will be trigger every time a backup has some change. So there is behavior difference.

In the future, I think the time-base sync process can be replaced by Reconcile way. The controller can sync just the changed backup in the Reconcile function, instead of whole backups in cluster. This is a more Kubernetes or event-driven way.

The advantages are:

• break down the batch sync task into small ones. If there is a lot of backups in cluster, this way has better performance.
• More timely backup sync. After the backup change event occurs, the sync is triggered, rather than to wait for 30s sync period.

But due to the coming FC date, revert first, then doing the job in future release is more reasonable.

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