simplify extension's registrations apis

Signed-off-by: Roman <ixrock@gmail.com>

extensions/example-extension/renderer.tsx

@@ -3,24 +3,14 @@ import { ExampleIcon, ExamplePage } from "./page"
 import React from "react"
 
 export default class ExampleExtension extends LensRendererExtension {
-  onActivate() {
-    console.log('EXAMPLE EXTENSION RENDERER: ACTIVATED', this.getMeta());
-  }
-
-  registerClusterPage() {
-    return [
-      {
-        path: "/extension-example",
-        title: "Example Extension",
-        components: {
-          Page: () => <ExamplePage extension={this} />,
-          MenuIcon: ExampleIcon,
-        }
+  clusterPages = [
+    {
+      path: "/extension-example",
+      title: "Example Extension",
+      components: {
+        Page: () => <ExamplePage extension={this}/>,
+        MenuIcon: ExampleIcon,
       }
-    ]
-  }
-
-  onDeactivate() {
-    console.log('EXAMPLE EXTENSION RENDERER: DEACTIVATED', this.getMeta());
-  }
+    }
+  ]
 }