DDC-3914: [GH-1515] [DDC-3146] Remove event listener from abstract hydrator in cleanup function

[doctrinebot]

Jira issue originally created by user @doctrinebot:

This issue is created automatically through a Github pull request on behalf of emiel-silverstreet:

Url: #1515

Message:

When the iterate function is invoked an event listener is added, but never removed. This will keep a reference to the abstract hydrator in the event manager, which will prevent the php garbage collector from removing the instance. When used multiple times this will create a memory leak because the event manager will be filled with references to unused hydrators. This fix will remove the event listener in the cleanup function which is invoked when the hydrator is finished, allowing the class to be garbage collected.