Once this completes, no more notifies will be sent to us for this
watch. This should be called to clean up unneeded watchers.
@param io the pool the object is in
@param completion what to do when operation has been attempted
@param cookie which watch to unregister
@returns 0 on success, negative error code on failure
Asynchronous unregister an interest in an object
Once this completes, no more notifies will be sent to us for this watch. This should be called to clean up unneeded watchers.
@param io the pool the object is in @param completion what to do when operation has been attempted @param cookie which watch to unregister @returns 0 on success, negative error code on failure