Jenkins - Remove old builds from Jenkins from all Jobs

purge.groovy

for(item in Jenkins.instance.items) {
    println("Deleting builds of job "+item.name)
    counter = 1
    for(build in item.getBuilds()){
        if(counter > 5){
            println("Delete " + build.number)
              try{
       		build.delete()
                  }catch(Exception e){
                   println(e.getMessage())
                  }
              }else{
                println("Skip " + build.number)
              }
        counter++
    }  
}