Remove unused --plot-angle variable, conditionally apply rotation in @place

Author: yuanchuan

src/property.js

@@ -66,8 +66,7 @@ export default add_alias({
       margin-left: calc(${cw} / -2);
       margin-top: calc(${ch} / -2);
       grid-area: unset;
-      --plot-angle: ${extra || 0};
-      rotate: ${extra || 0}deg;
+      ${extra ? `rotate: ${extra || 0}deg`: ''}
     `;
   },