Geomap: hide legend for markers with single threshold (#38734) (#38738)

(cherry picked from commit f567bef0bf)

Co-authored-by: Ryan McKinley <ryantxu@gmail.com>

public/app/plugins/panel/geomap/layers/data/MarkersLegend.tsx

@@ -46,8 +46,8 @@ export function MarkersLegend(props: MarkersLegendProps) {
   }
 
   const thresholds = color.field?.config?.thresholds;
-  if (!thresholds) {
-    return <div className={style.infoWrap}>no thresholds????</div>;
+  if (!thresholds || thresholds.steps.length < 2) {
+    return <div></div>; // don't show anything in the legend
   }
 
   return (