Simplify AnyScript

[jglick]

Simplifying a rather roundabout system to just be like

pipeline-model-definition-plugin/pipeline-model-definition/src/main/resources/org/jenkinsci/plugins/pipeline/modeldefinition/agent/impl/LabelScript.groovy

Lines 41 to 45 in 12b420f

	return {
	script.node(describable?.label) {
	CheckoutScript.doCheckout(script, describable, describable.customWorkspace, body).call()
	}
	}

except without the label and customWorkspace fields. The weird logic seems to have been introduced in #94, at which time perhaps it made sense but it seems CheckoutScript when introduced in #123 was not also used here.

[jglick]

Note two methods which are no longer used in non-test code in this plugin but still used in https://github.com/jenkinsci/docker-workflow-plugin/blob/c7dedefcf68f6ce1320c8aaaeb831628ea21a086/src/main/java/org/jenkinsci/plugins/docker/workflow/declarative/DeclarativeDockerUtils.java#L91-L92 which could probably also be simplified along similar lines though I am not inclined to spend time on that plugin.

The analogous code in kubernetes is already straightforward: https://github.com/jenkinsci/kubernetes-plugin/blob/44fee1844a33a5946bf9f721edb9da64b7b7b3da/src/main/resources/org/csanchez/jenkins/plugins/kubernetes/pipeline/KubernetesDeclarativeAgentScript.groovy#L52-L53

[jglick]

(Desired for #533.)

[jtnord]

as far as I understand this code, I see nothing obviously wrong