quick open: remove unused "checked" option and related CSS

src/vs/workbench/browser/parts/quickopen/media/check-inverse.svg

@@ -1 +0,0 @@
-<svg xmlns="http://www.w3.org/2000/svg" width="16" height="16"><path d="M12 4l-4 8h-2l-2-4h2l1 2 3-6h2z" fill="#81A632"/></svg>

src/vs/workbench/browser/parts/quickopen/media/check.svg

@@ -1 +0,0 @@
-<svg xmlns="http://www.w3.org/2000/svg" width="16" height="16"><path d="M12 4l-4 8h-2l-2-4h2l1 2 3-6h2z" fill="#7FBA00"/></svg>

src/vs/workbench/browser/parts/quickopen/media/quickopen.css

@@ -3,20 +3,6 @@
  *  Licensed under the MIT License. See License.txt in the project root for license information.
  *--------------------------------------------------------------------------------------------*/
 
-.vs .quick-open-widget .quick-open-tree .quick-open-entry .quick-open-entry-icon.checked {
-	background: url("check.svg") center center no-repeat;
-	width: 16px;
-	height: 16px;
-	vertical-align: text-bottom;
-}
-
-.vs-dark .quick-open-widget .quick-open-tree .quick-open-entry .quick-open-entry-icon.checked {
-	background: url("check-inverse.svg") center center no-repeat;
-	width: 16px;
-	height: 16px;
-	vertical-align: text-bottom;
-}
-
 .vs .quick-open-widget .quick-open-tree .quick-open-entry .quick-open-entry-icon.none,
 .vs-dark .quick-open-widget .quick-open-tree .quick-open-entry .quick-open-entry-icon.none {
 	width: 16px;

src/vs/workbench/services/quickopen/browser/quickOpenService.ts

@@ -13,7 +13,6 @@ import {IEditorInput} from 'vs/platform/editor/common/editor';
 
 export interface IPickOpenEntry {
 	id?: string;
-	checked?: boolean;
 	label: string;
 	description?: string;
 }