Do not redirect to referer when updating the labels jar.

The referer is usually the form submitting the change.
But we want to redirect to the default view of the current context.

Background:
- The refere, redirecting back to the submitting form, may be invalid because the label ID is missing.
- ftw.testbrowser now [submits the referer correctly](https://github.com/4teamwork/ftw.testbrowser/commit/4f5a6863ac467c68bbf4c039b5d5559f823b84ed), which exposed this problem.
- The problem was not visible in production since we do AJAX requests and the redirect is not relevant because the overlay with the form is closed - the production keeps the same behavior.