message: fix(legacy-plugin-chart-sankey-loop): clear element before redrawing
  otherwise every (re)render adds a new svg to the element. this is essentially
  the same as the fix that was applied to legacy-plugin-chart-sankey back in
  apache/superset#254
diff: @@ -98,7 +98,10 @@ function SankeyLoop(element, props) {
  )
  .linkColor(d => color(d.source.name));
  - const svg = select(element)
  + const div = select(element);
  + div.selectAll('*').remove();
  +
  + const svg = div
  .append('svg')
  .classed('superset-legacy-chart-sankey-loop', true)
  .style('width', width)
  