Using code from comments above, I have a Jenkins job that runs weekly to remove the ones that start with certain phrases. This may have race conditions (see later comments):

stage ("JENKINS-38906") {
  def manager = org.jenkins.plugins.lockableresources.LockableResourcesManager.get()
  def resources = manager.getResources().findAll {
      (!it.locked) && (
          it.name.startsWith("docker_rpminstalled") ||
          it.name.startsWith("docker-rpmbuild") ||
          it.name.startsWith("rpm-deploy")
      )
  }
  currentBuild.description = "${resources.size()} locks"
  resources.each {
      println "Removing ${it.name}"   
      manager.getResources().remove(it)
  }
  manager.save()
} // stage

Aaron D. Marasco You should synchronize access to LocalbleResouceManager, otherwise you might cause race condition. Considering LocakbleResourcesManager relies on synchronization, it should actually be a trivial task to delete lock after it has been released.

We're using this to delete locks after our ansible plays:

@NonCPS
def deleteLocks(lockNames) {
  def manager = org.jenkins.plugins.lockableresources.LockableResourcesManager.get()
  synchronized (manager) {
    manager.getResources().removeAll { r -> lockNames.contains(r.name) && !r.locked && !r.reserved }
    manager.save()
  }
}

 Edit: I had time to study problem further. While this does resolve race condition when deleting item from list, it still isn't sufficient. Current lock allocation algorithm relies that locks are not deleted in any way. I think that's something I can fix. However I think that algorithm needs major rework. Everything related lock management has to be done with atomic operations - and to do so, management must be done in a single class. There might be some scalability issues when allocating hundreds of locks, that could be resolved as well.

Thanks Sami Korhonen for the heads-up. I don't need to worry about race conditions in my unique situation. However, I'll make a note in case others just see it and copypasta.

This should be fixed with the ephemeral lock support in release 2.6 - Everthing that is created automatically is now removed automatically.