Remove same-origin-data-url flag from fetch implementation

The spec removed it. Check the scheme instead, data is always same origin now,
except for workers.
This also updates the comments to make step numbers match the spec.
Closes #13362

components/script/fetch.rs

@@ -44,7 +44,6 @@ fn request_init_from_request(request: NetTraitsRequest) -> NetTraitsRequestInit
         url: request.url(),
         headers: request.headers.borrow().clone(),
         unsafe_request: request.unsafe_request,
-        same_origin_data: request.same_origin_data.get(),
         body: request.body.borrow().clone(),
         type_: request.type_,
         destination: request.destination,