fix compilation

src/vs/workbench/parts/debug/electron-browser/watchExpressionsView.ts

@@ -26,7 +26,7 @@ import { VariablesRenderer, variableSetEmitter } from 'vs/workbench/parts/debug/
 import { IContextKeyService } from 'vs/platform/contextkey/common/contextkey';
 import { WorkbenchAsyncDataTree, IListService } from 'vs/platform/list/browser/listService';
 import { IThemeService } from 'vs/platform/theme/common/themeService';
-import { IAsyncDataSource, ITreeMouseEvent, ITreeContextMenuEvent, ITreeDragAndDrop, ITreeDragOverReaction, ITreeElement } from 'vs/base/browser/ui/tree/tree';
+import { IAsyncDataSource, ITreeMouseEvent, ITreeContextMenuEvent, ITreeDragAndDrop, ITreeDragOverReaction } from 'vs/base/browser/ui/tree/tree';
 import { IDragAndDropData } from 'vs/base/browser/dnd';
 import { onUnexpectedError } from 'vs/base/common/errors';