remove unused code and irrelevant comment

Author: sryza

sql/pipelines/src/main/scala/org/apache/spark/sql/pipelines/graph/PipelineExecution.scala

@@ -17,8 +17,6 @@
 
 package org.apache.spark.sql.pipelines.graph
 
-import scala.annotation.unused
-
 import org.apache.spark.sql.pipelines.logging.{
   ConstructPipelineEvent,
   EventLevel,
@@ -115,17 +113,4 @@ class PipelineExecution(context: PipelineUpdateContext) {
       )
     }
   }
-
-  @unused(
-    "TODO(SPARK-51727): connect this API with spark connect backend and expose it to the user"
-  )
-  def stopPipeline(): Unit = synchronized {
-    graphExecution
-      .getOrElse(
-        throw new IllegalStateException(
-          "Pipeline execution has not started yet."
-        )
-      )
-      .stop()
-  }
 }

sql/pipelines/src/main/scala/org/apache/spark/sql/pipelines/graph/TriggeredGraphExecution.scala

@@ -110,7 +110,7 @@ class TriggeredGraphExecution(
     val thread = buildTopologicalExecutionThread()
     UncaughtExceptionHandler.addHandler(
       thread, {
-        case _: InterruptedException => // stop from UI leads to InterruptedException. Do nothing.
+        case _: InterruptedException =>
         case _ =>
           try {
             stopInternal(stopTopologicalExecutionThread = false)