Always request hex via the post to API mechanism (#3149)

* Always request hex via the post to API mechanism

- enables logging of requests for older versions via API rather than GA,
- gives flexibility in future if we need to return alternative hex files for any reason.

* The URL for the hex is now returned by the API

* Only apply these settings if expertmode is enabled.

src/js/release_loader.js

@@ -90,7 +90,6 @@ class ReleaseLoader {
             contentType: "application/json",
             dataType: "json",
             success: function(data) {
-                data.url = `/api/builds/${data.key}/hex`;
                 onSuccess(data);
             },
         }).fail(xhr => {