message: fix: remove sticky tooltip when query returns no data in explore view
  Tap into the newly added `willUnmount` hook to clean up sticky tooltip that nvd3 adds to `body` directly. This removes such tooltips that were left behind in the explore view with the new query returns 'no data'.
diff: */
  import { reactify } from '@superset-ui/chart';
  import Component from './NVD3Vis';
  +import { hideTooltips } from './utils';
  -export default reactify(Component);
  +function willUnmount() {
  + hideTooltips(true);
  +}
  +
  +export default reactify(Component, { willUnmount });
  