GroovyClosureScript can be replaced with groovy.util.DelegatingScript

[jvz]

https://github.com/stapler/stapler/blob/11ad5af185e062fb46e01bf9fbed66f3ebf2a8f7/groovy/src/main/java/org/kohsuke/stapler/jelly/groovy/GroovyClosureScript.java#L63

I just noticed this while working on a similar parser to this for Log4j configurations. It seems as though Groovy eventually added a class that's almost exactly the same as the one in Stapler.