[MINOR][CORE] Quiet request executor remove message

### What changes were proposed in this pull request?

Settings to quiet for Class `ExecutorAllocationManager` that request message too verbose. otherwise, this class generates too many messages like
`INFO spark.ExecutorAllocationManager: Request to remove executorIds: 890`
 when we enabled DRA.

### Why are the changes needed?

Log level improvement.

### Does this PR introduce any user-facing change?

No

### How was this patch tested?

Closes apache#26925 from cfmcgrady/quiet-request-executor-remove-message.

Authored-by: Fu Chen <cfmcgrady@gmail.com>
Signed-off-by: Sean Owen <srowen@gmail.com>

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

@@ -423,7 +423,7 @@ private[spark] class ExecutorAllocationManager(
   private def removeExecutors(executors: Seq[String]): Seq[String] = synchronized {
     val executorIdsToBeRemoved = new ArrayBuffer[String]
 
-    logInfo("Request to remove executorIds: " + executors.mkString(", "))
+    logDebug(s"Request to remove executorIds: ${executors.mkString(", ")}")
     val numExistingExecutors = executorMonitor.executorCount - executorMonitor.pendingRemovalCount
 
     var newExecutorTotal = numExistingExecutors