Jenkins delete old build for job via Script Console

script.groovy

import jenkins.model.Jenkins
import hudson.model.Job

MAX_BUILDS = 5
Jenkins.instance.getAllItems(Job.class).each { job ->
  if (job.fullName == 'DatabaseDocker/master') {
    println job.fullName
  	def recent = job.builds.limit(MAX_BUILDS)
    for (build in job.builds) {
      if (!recent.contains(build)) {
        println "Preparing to delete: " + build
        // build.delete()
      }
    }
  }
}

println "============= DONE ============="

if you want to REALLY delete your build - uncomment // build.delete() line