Concurrent `delete subscription` and `delete topic` lead to memory leak

[hezhangjian]

Describe the bug
Concurrent request delete subscription A and delete topic B will lead to leak ManagerLedgerImpl、ManagerCursorImpl、and any object related to them leak.
That's the work flow

Step1

A delete the cursor ledger.asyncDeleteCursor, but don't remove the subscription from ConcurrentOpenHashMap<String, PersistentSubscription> subscriptions;

Step2

Second, B delete the topic, as long as the subscription in subscriptions, B try to delete the cursor. Because of the cursor already been delete in Step1, delete topic failed

Step3

A remove the subscrption from subscriptions

That lead to memory leak, can't free ManagerLedgerImpl、ManagerCursorImpl、and any object related to them.