Remove samples (#22288)

Add code, that was used for documentation to the appropriate projects
or akka-docs.

akka-docs/rst/scala/code/docs/persistence/PersistentActorExample.scala

@@ -0,0 +1,60 @@
+package scala.docs.persistence
+
+//#persistent-actor-example
+import akka.actor._
+import akka.persistence._
+
+case class Cmd(data: String)
+case class Evt(data: String)
+
+case class ExampleState(events: List[String] = Nil) {
+  def updated(evt: Evt): ExampleState = copy(evt.data :: events)
+  def size: Int = events.length
+  override def toString: String = events.reverse.toString
+}
+
+class ExamplePersistentActor extends PersistentActor {
+  override def persistenceId = "sample-id-1"
+
+  var state = ExampleState()
+
+  def updateState(event: Evt): Unit =
+    state = state.updated(event)
+
+  def numEvents =
+    state.size
+
+  val receiveRecover: Receive = {
+    case evt: Evt                                 => updateState(evt)
+    case SnapshotOffer(_, snapshot: ExampleState) => state = snapshot
+  }
+
+  val receiveCommand: Receive = {
+    case Cmd(data) =>
+      persist(Evt(s"${data}-${numEvents}"))(updateState)
+      persist(Evt(s"${data}-${numEvents + 1}")) { event =>
+        updateState(event)
+        context.system.eventStream.publish(event)
+      }
+    case "snap"  => saveSnapshot(state)
+    case "print" => println(state)
+  }
+
+}
+//#persistent-actor-example
+
+object PersistentActorExample extends App {
+
+  val system = ActorSystem("example")
+  val persistentActor = system.actorOf(Props[ExamplePersistentActor], "persistentActor-4-scala")
+
+  persistentActor ! Cmd("foo")
+  persistentActor ! Cmd("baz")
+  persistentActor ! Cmd("bar")
+  persistentActor ! "snap"
+  persistentActor ! Cmd("buzz")
+  persistentActor ! "print"
+
+  Thread.sleep(10000)
+  system.terminate()
+}