Remove obsolete plugin configuration

The empty objects in the default config only exist to ensure that the
corresponding plugin is initialized in the `Guest` constructor.

Some of these are obsolete:

 - There is no longer a `TextSelection` plugin

 - There is no longer a `Toolbar` plugin

 - The `Document` plugin only needs to be initialized in the `Guest`
   base class

src/annotator/guest.js

@@ -67,11 +67,9 @@ const IGNORE_SELECTOR = '[class^="annotator-"],[class^="hypothesis-"]';
 
 export default class Guest extends Delegator {
   constructor(element, config, anchoring = htmlAnchoring) {
-    // TODO - Find out if `defaultConfig` actually does anything and remove it
-    // if not.
     const defaultConfig = {
+      // This causes the `Document` plugin to be initialized.
       Document: {},
-      TextSelection: {},
     };
 
     super(element, { ...defaultConfig, ...config });

src/annotator/pdf-sidebar.js

@@ -6,15 +6,11 @@ import Sidebar from './sidebar';
  */
 
 const defaultConfig = {
-  TextSelection: {},
   PDF: {},
   BucketBar: {
     container: '.annotator-frame',
     scrollables: ['#viewerContainer'],
   },
-  Toolbar: {
-    container: '.annotator-frame',
-  },
 };
 
 // The viewport and controls for PDF.js start breaking down below about 670px

src/annotator/sidebar.js

@@ -19,8 +19,6 @@ import { ToolbarController } from './toolbar';
 const MIN_RESIZE = 280;
 
 const defaultConfig = {
-  Document: {},
-  TextSelection: {},
   BucketBar: {
     container: '.annotator-frame',
   },