[ENHANCEMENT] DistributedDeletedMessageVaultDeletionCallback should b…

…e singleton

server/container/guice/distributed/src/main/java/org/apache/james/modules/mailbox/DistributedDeletedMessageVaultModule.java

@@ -67,6 +67,7 @@ protected void configure() {
         Multibinder.newSetBinder(binder(), DeleteMessageListener.DeletionCallback.class)
             .addBinding()
             .to(DistributedDeletedMessageVaultDeletionCallback.class);
+        bind(DistributedDeletedMessageVaultDeletionCallback.class).in(Scopes.SINGLETON);
     }
 
     @ProvidesIntoSet