AutorecoveringConnection.maybeDeleteRecordedAutoDeleteExchange does not need to acquire a lock on this.consumers

It most likely was a copy-paste artefact introduced back in 2013-2014.
AutorecoveringConnection.maybeDeleteRecordedAutoDeleteQueue does need
to lock this.consumers as conditional queue deletion does need to
check the number of known consumers on that queue.

1aad565 addressed a potential deadlock caused by the unsafe
order of lock acquisitions. In #648 another similar issue
was discovered which #649 tried to address by acquiring a lock
on this.consumers early.

However, exchange cleanup does not need to lock this.consumers
as it does not mutate it.

Closes #648.

(cherry picked from commit 5c3fce8)

Author: michaelklishin

src/main/java/com/rabbitmq/client/impl/recovery/AutorecoveringConnection.java

@@ -1032,15 +1032,13 @@ void maybeDeleteRecordedAutoDeleteQueue(String queue) {
     }
 
     void maybeDeleteRecordedAutoDeleteExchange(String exchange) {
-        synchronized (this.consumers) {
-            synchronized (this.recordedExchanges) {
-                if(!hasMoreDestinationsBoundToExchange(Utility.copy(this.recordedBindings), exchange)) {
-                    RecordedExchange x = this.recordedExchanges.get(exchange);
-                    // last binding where this exchange is the source is gone, remove recorded exchange
-                    // if it is auto-deleted. See bug 26364.
-                    if(x != null && x.isAutoDelete()) {
-                        deleteRecordedExchange(exchange);
-                    }
+        synchronized (this.recordedExchanges) {
+            if(!hasMoreDestinationsBoundToExchange(Utility.copy(this.recordedBindings), exchange)) {
+                RecordedExchange x = this.recordedExchanges.get(exchange);
+                // last binding where this exchange is the source is gone, remove recorded exchange
+                // if it is auto-deleted. See bug 26364.
+                if(x != null && x.isAutoDelete()) {
+                    deleteRecordedExchange(exchange);
                 }
             }
         }