src/vs/workbench/contrib/notebook/browser/notebookEditorServiceImpl.ts/NotebookEditorWidgetService/removeNotebookEditor
class NotebookEditorWidgetService:	removeNotebookEditor(editor: INotebookEditor): void {
		if (this._notebookEditors.has(editor.getId())) {
			this._notebookEditors.delete(editor.getId());
			this._onNotebookEditorsRemove.fire(editor);
		}
	}