Lib: Remove non-lazy image

We need the width/height anyways to determine the max size, so don't
bother with non-lazy stuff

src/lib/components/form/Dropdown.ts

@@ -7,4 +7,10 @@ export interface DropdownOption {
 
   /** An optional icon displayed left to the label */
   icon_url?: string;
+
+  /** The icon width. Required if icon_url is set */
+  icon_width?: number;
+
+  /** The icon height. Required if icon_url is set */
+  icon_height?: number;
 }