scheduler: remove reservation nominator useless code

[xulinfei1996]

Ⅰ. Describe what this PR does

If Reservation is Active, Failed or Succeed, it must be scheduled after it triggers preemption, so its nominated information will be deleted in this round schedule process. As in the framework, it will exec DeleteNominatedReservePod in RunReservePluginsReserve.
In a conclusion, it is no need to DeleteReservePod in ReservationHandler OnUpdate handler.

Ⅱ. Does this pull request fix one issue?

Ⅲ. Describe how to verify it

Ⅳ. Special notes for reviews

V. Checklist

• I have written necessary docs and comments
• I have added necessary unit tests and integration tests
• All checks passed in make test

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[saintube]

Ⅰ. Describe what this PR does

If Reservation is Active, Failed or Succeed, it must be scheduled after it triggers preemption, so its nominated information will be deleted in this round schedule process.

AFAIK, the reservation would not get scheduled (enqueue the SchedulingQueue) when its phase becomes Available, Failed, or Succeeded. Besides, deleting an unreserved reservation pod in the nominator seems idempotent. So I'm wondering if removing the deletion of the nominated reservation is correct and required.