fix: correct EventBus#off type definition

Adding generic (unknown) type is necessary in recent TypeScript versions.

lib/core/EventBus.js

@@ -269,7 +269,7 @@ EventBus.prototype.once = function(events, priority, callback, that) {
  * If no callback is given, all listeners for a given event name are being removed.
  *
  * @param {string|string[]} events
- * @param {EventBusEventCallback} [callback]
+ * @param {EventBusEventCallback<unknown>} [callback]
  */
 EventBus.prototype.off = function(events, callback) {