fix(ui/side_panel) biome linter broke drag end handler (#527)

* fix(ui/side_panel) biome linter broke drag end handler

* disabled biome noDelete option

Author: chrisj

biome.json

@@ -59,6 +59,9 @@
       "correctness": {
         "useYield": "off",
         "noUnsafeFinally": "off"
+      },
+      "performance": {
+        "noDelete": "off"
       }
     }
   }

src/ui/side_panel.ts

@@ -280,7 +280,7 @@ export class SidePanelManager extends RefCounted {
   }
 
   endDrag() {
-    this.element.dataset.neuroglancerSidePanelDrag = undefined;
+    delete this.element.dataset.neuroglancerSidePanelDrag;
     this.dragSource = undefined;
   }