USD export: ignore selected-only for dome lights

Updated the dome light export logic to disregard the selected-only
option, since the world material can't be selected as an object.

Pull Request: https://projects.blender.org/blender/blender/pulls/123199

source/blender/io/usd/intern/usd_capi_export.cc

@@ -428,7 +428,7 @@ pxr::UsdStageRefPtr export_to_stage(const USDExportParams &params,
   /* Creating dome lights should be called after writers have
    * completed, to avoid a name collision when creating the light
    * prim. */
-  if (!params.selected_objects_only && params.convert_world_material) {
+  if (params.convert_world_material) {
     world_material_to_dome_light(params, scene, usd_stage);
   }