revert spurious test change; this came from another PR

sql/core/src/test/scala/org/apache/spark/sql/streaming/continuous/ContinuousSuite.scala

@@ -21,7 +21,6 @@ import java.io.{File, InterruptedIOException, IOException, UncheckedIOException}
 import java.nio.channels.ClosedByInterruptException
 import java.util.concurrent.{CountDownLatch, ExecutionException, TimeoutException, TimeUnit}
 
-import scala.collection.mutable
 import scala.reflect.ClassTag
 import scala.util.control.ControlThrowable
 
@@ -30,7 +29,7 @@ import org.apache.commons.io.FileUtils
 import org.apache.hadoop.conf.Configuration
 
 import org.apache.spark.{SparkContext, SparkEnv}
-import org.apache.spark.scheduler.{SparkListener, SparkListenerJobStart, SparkListenerTaskEnd, SparkListenerTaskStart}
+import org.apache.spark.scheduler.{SparkListener, SparkListenerJobStart}
 import org.apache.spark.sql._
 import org.apache.spark.sql.catalyst.plans.logical.Range
 import org.apache.spark.sql.catalyst.streaming.InternalOutputModes
@@ -246,29 +245,6 @@ class ContinuousSuite extends ContinuousSuiteBase {
 class ContinuousStressSuite extends ContinuousSuiteBase {
   import testImplicits._
 
-  // Continuous processing tasks end asynchronously, so test that they actually end.
-  private val tasksEndedListener = new SparkListener() {
-    val activeTaskIds = mutable.Set[Long]()
-
-    override def onTaskStart(start: SparkListenerTaskStart): Unit = {
-      activeTaskIds.add(start.taskInfo.taskId)
-    }
-
-    override def onTaskEnd(end: SparkListenerTaskEnd): Unit = {
-      activeTaskIds.remove(end.taskInfo.taskId)
-    }
-  }
-  override def beforeEach(): Unit = {
-    spark.sparkContext.addSparkListener(tasksEndedListener)
-  }
-
-  override def afterEach(): Unit = {
-    eventually(timeout(streamingTimeout)) {
-      assert(tasksEndedListener.activeTaskIds.isEmpty)
-    }
-    spark.sparkContext.removeSparkListener(tasksEndedListener)
-  }
-
   test("only one epoch") {
     val df = spark.readStream
       .format("rate")