[SPARK-26788][yarn] Remove SchedulerExtensionService.

core/src/main/scala/org/apache/spark/SparkConf.scala

@@ -638,7 +638,8 @@ private[spark] object SparkConf extends Logging {
       DeprecatedConfig("spark.shuffle.service.index.cache.entries", "2.3.0",
         "Not used anymore. Please use spark.shuffle.service.index.cache.size"),
       DeprecatedConfig("spark.yarn.credentials.file.retention.count", "2.4.0", "Not used anymore."),
-      DeprecatedConfig("spark.yarn.credentials.file.retention.days", "2.4.0", "Not used anymore.")
+      DeprecatedConfig("spark.yarn.credentials.file.retention.days", "2.4.0", "Not used anymore."),
+      DeprecatedConfig("spark.yarn.services", "3.0.0", "Feature no longer available.")
     )
 
     Map(configs.map { cfg => (cfg.key -> cfg) } : _*)

resource-managers/yarn/src/main/scala/org/apache/spark/deploy/yarn/config.scala

@@ -181,12 +181,6 @@ package object config {
       .timeConf(TimeUnit.MILLISECONDS)
       .createWithDefaultString("200ms")
 
-  private[spark] val SCHEDULER_SERVICES = ConfigBuilder("spark.yarn.services")
-    .doc("A comma-separated list of class names of services to add to the scheduler.")
-    .stringConf
-    .toSequence
-    .createWithDefault(Nil)
-
   private[spark] val AM_FINAL_MSG_LIMIT = ConfigBuilder("spark.yarn.am.finalMessageLimit")
     .doc("The limit size of final diagnostic message for our ApplicationMaster to unregister from" +
       " the ResourceManager.")

resource-managers/yarn/src/main/scala/org/apache/spark/scheduler/cluster/YarnSchedulerBackend.scala

@@ -73,10 +73,6 @@ private[spark] abstract class YarnSchedulerBackend(
   /** Attempt ID. This is unset for client-mode schedulers */
   private var attemptId: Option[ApplicationAttemptId] = None
 
-  /** Scheduler extension services. */
-  private val services: SchedulerExtensionServices = new SchedulerExtensionServices()
-
-
   /**
    * Bind to YARN. This *must* be done before calling [[start()]].
    *
@@ -90,8 +86,6 @@ private[spark] abstract class YarnSchedulerBackend(
 
   protected def startBindings(): Unit = {
     require(appId.isDefined, "application ID unset")
-    val binding = SchedulerExtensionServiceBinding(sc, appId.get, attemptId)
-    services.start(binding)
   }
 
   override def stop(): Unit = {
@@ -102,7 +96,6 @@ private[spark] abstract class YarnSchedulerBackend(
       super.stop()
     } finally {
       stopped.set(true)
-      services.stop()
     }
   }