[fix][meta] Fix close borrowed executor (#19761)

(cherry picked from commit 710cea6)

Author: mattisonchao

pulsar-metadata/src/main/java/org/apache/pulsar/metadata/coordination/impl/LeaderElectionImpl.java

@@ -253,8 +253,6 @@ public synchronized CompletableFuture<Void> asyncClose() {
 
         internalState = InternalState.Closed;
 
-        executor.shutdownNow();
-
         if (leaderElectionState != LeaderElectionState.Leading) {
             return CompletableFuture.completedFuture(null);
         }