Remove stateful processors from the script processor (elastic#16514)

There are some processors that keep resources that would need to be
explicitly released when the processor is not needed anymore. At this
moment there is no way to do it, processors have a stateless interface,
so avoid using these processors in scripts.

If these processors are needed, it is usually better to place them in
global configuration.

Processors removed are the ones used to add docker and kubernetes
metadata.

(cherry picked from commit 8d31a51)

CHANGELOG.next.asciidoc

@@ -23,6 +23,7 @@ https://github.com/elastic/beats/compare/v7.0.0-alpha2...master[Check the HEAD d
 - The document id fields has been renamed from @metadata.id to @metadata._id {pull}15859[15859]
 - Variable substitution from environment variables is not longer supported. {pull}15937{15937}
 - Change aws_elb autodiscover provider field name from elb_listener.* to aws.elb.*. {issue}16219[16219] {pull}16402{16402}
+- Remove `AddDockerMetadata` and `AddKubernetesMetadata` processors from the `script` processor. They can still be used as normal processors in the configuration. {issue}16349[16349] {pull}16514[16514]
 
 *Auditbeat*
 

libbeat/processors/add_docker_metadata/add_docker_metadata.go

@@ -37,7 +37,6 @@ import (
 	"github.com/elastic/beats/libbeat/logp"
 	"github.com/elastic/beats/libbeat/processors"
 	"github.com/elastic/beats/libbeat/processors/actions"
-	jsprocessor "github.com/elastic/beats/libbeat/processors/script/javascript/module/processor"
 )
 
 const (
@@ -52,7 +51,6 @@ var processCgroupPaths = cgroup.ProcessCgroupPaths
 
 func init() {
 	processors.RegisterPlugin(processorName, New)
-	jsprocessor.RegisterPlugin("AddDockerMetadata", New)
 }
 
 type addDockerMetadata struct {

libbeat/processors/add_kubernetes_metadata/kubernetes.go

@@ -33,7 +33,6 @@ import (
 	"github.com/elastic/beats/libbeat/common/kubernetes/metadata"
 	"github.com/elastic/beats/libbeat/logp"
 	"github.com/elastic/beats/libbeat/processors"
-	jsprocessor "github.com/elastic/beats/libbeat/processors/script/javascript/module/processor"
 )
 
 const (
@@ -54,7 +53,6 @@ type kubernetesAnnotator struct {
 
 func init() {
 	processors.RegisterPlugin("add_kubernetes_metadata", New)
-	jsprocessor.RegisterPlugin("AddKubernetesMetadata", New)
 
 	// Register default indexers
 	Indexing.AddIndexer(PodNameIndexerName, NewPodNameIndexer)