Re-fix OpenID requests from widgets
https://github.com/matrix-org/matrix-react-sdk/pull/4591 reverted
https://github.com/matrix-org/matrix-react-sdk/pull/4459. We need
to pass both URLs as we need both the wURL (for the widget's 'identity'
ie. OpenID) and the URL that's actually in the iframe (for the
messaging).
