Remove Launcher chainer from JobSet plugin

[tenzen-y]

What you would like to be added?

Once #2502 is resolved, we can remove Launcher chainer function from JobSet plugin since validations always check the rJob replicas.

trainer/pkg/runtime/framework/plugins/jobset/builder.go

Lines 104 to 114 in 4b0c294

	// Launcher updates JobSet values for the launcher Job.
	func (b *Builder) Launcher(info *runtime.Info, trainJob *trainer.TrainJob) *Builder {
	for i, rJob := range b.Spec.ReplicatedJobs {
	if *rJob.Name == constants.Launcher {
	// TODO: Support multiple replicas ('.template.spec.replicatedJobs[*].replicas') for replicated Jobs.
	// REF: https://github.com/kubeflow/trainer/issues/2318
	b.Spec.ReplicatedJobs[i].Replicas = ptr.To[int32](1)
	}
	}
	return b
	}

trainer/pkg/runtime/framework/plugins/jobset/jobset.go

Line 197 in 4b0c294

Launcher(info, trainJob).

Why is this needed?

Validations always check the rJob replicas.
So, overriding the Lacunher replicas is not needed.

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[tenzen-y]

@IRONICBo Would you mind taking this issue? After your current PR, this will be unblocked.

[IRONICBo]

@tenzen-y Yes, I want to take it.

[IRONICBo]

/assign

[tenzen-y]

@tenzen-y Yes, I want to take it.

Thank you