ui: Don't show filters when there is only one item

static/lib.js

@@ -208,9 +208,13 @@ class TimeseriesGraph extends HTMLElement {
         // We need to maintain a stable order for these
         var children = [];
         for (var key of Object.keys(this.#filterLabels).sort()) {
+            // If there are multiple items to filter by then show the selectElement.
+            // otherwise there is no point.
+            if (this.#filterLabels[key].length > 1) {
                 const element = this.#filterSelectElements[key] || this.buildSelectElement(key);
                 children.push(element);
             }
+        }
         this.#menuContainer.replaceChildren(...children);
     }