Simplify events and store listeners only in one place

src/ol/events/Event.js

@@ -12,7 +12,7 @@
  * for higher level events defined in the library, and works with
  * {@link module:ol/events/Target~Target}.
  */
-class Event {
+class BaseEvent {
 
   /**
    * @param {string} type Type.
@@ -73,4 +73,4 @@ export function preventDefault(evt) {
   evt.preventDefault();
 }
 
-export default Event;
+export default BaseEvent;

src/ol/events/Target.js

@@ -2,9 +2,9 @@
  * @module ol/events/Target
  */
 import Disposable from '../Disposable.js';
-import {unlistenAll} from '../events.js';
 import {VOID} from '../functions.js';
 import Event from './Event.js';
+import {clear} from '../obj.js';
 
 
 /**
@@ -116,7 +116,7 @@ class Target extends Disposable {
    * @inheritDoc
    */
   disposeInternal() {
-    unlistenAll(this);
+    clear(this.listeners_);
   }
 
   /**