Remove unused import

src/vs/base/browser/ui/tree/abstractTree.ts

@@ -7,7 +7,7 @@ import 'vs/css!./media/tree';
 import { IDisposable, dispose, Disposable, toDisposable } from 'vs/base/common/lifecycle';
 import { IListOptions, List, IListStyles, mightProducePrintableCharacter, MouseController } from 'vs/base/browser/ui/list/listWidget';
 import { IListVirtualDelegate, IListRenderer, IListMouseEvent, IListEvent, IListContextMenuEvent, IListDragAndDrop, IListDragOverReaction, IKeyboardNavigationLabelProvider } from 'vs/base/browser/ui/list/list';
-import { append, $, toggleClass, getDomNodePagePosition, removeClass, addClass, hasClass, createStyleSheet } from 'vs/base/browser/dom';
+import { append, $, toggleClass, getDomNodePagePosition, removeClass, addClass, hasClass } from 'vs/base/browser/dom';
 import { Event, Relay, Emitter, EventBufferer } from 'vs/base/common/event';
 import { StandardKeyboardEvent, IKeyboardEvent } from 'vs/base/browser/keyboardEvent';
 import { KeyCode } from 'vs/base/common/keyCodes';