fixes Manager failing to properly remove event listeners from Connection

[david-hodgetts]

I believe there is a memory leak in the handling of event listeners in the Manager class.
The callbacks registered on the Connection object in the addEventListeners method are improperly removed in the removeEventListeners method.
The references to the callbacks are lost because they are modified by a call to the bind method. Each call to bind creates a new reference, see.

[jaakkos]

Good catch 👍 I didn't remember that while doing the change. I'll just run the extra checks; if they pass, I'll merge them.