Remove redundant ValidateInstanceGroup call

[rifelpet]

The cloudup.PopulateInstanceGroupSpec directly after this calls ValidateInstanceGroup so this first call is redundant.

kops/upup/pkg/fi/cloudup/populate_instancegroup_spec.go

Lines 61 to 66 in 7b06798

	func PopulateInstanceGroupSpec(cluster *kops.Cluster, input *kops.InstanceGroup, channel *kops.Channel) (*kops.InstanceGroup, error) {
	var err error
	err = validation.ValidateInstanceGroup(input).ToAggregate()
	if err != nil {
	return nil, err
	}

This is minor cleanup to help simplify the aws instance type validation PR

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[johngmyers]

Indeed.
/lgtm