fix(tests): BaseAnnotator test emitter leak

[ConradJChan]

Clean up the existing annotator before getting a new one.

This cleans up the following when running tests:

(node:6655) MaxListenersExceededWarning: Possible EventEmitter memory leak detected. 11 scaleannotations listeners added to [EventManager]. Use emitter.setMaxListeners() to increase limit
(node:6655) MaxListenersExceededWarning: Possible EventEmitter memory leak detected. 11 annotations_active_set listeners added to [EventManager]. Use emitter.setMaxListeners() to increase limit
(node:6655) MaxListenersExceededWarning: Possible EventEmitter memory leak detected. 11 annotations_remove listeners added to [EventManager]. Use emitter.setMaxListeners() to increase limit
(node:6655) MaxListenersExceededWarning: Possible EventEmitter memory leak detected. 11 annotations_visible_set listeners added to [EventManager]. Use emitter.setMaxListeners() to increase limit