oauth2: Don't add redirect_uri when grant_type=refresh_token
oauth2: Don't add redirect_uri when grant_type=refresh_token

Google complains loudly when we do so. See:
https://developers.google.com/accounts/docs/OAuth2InstalledApp#refresh

Fixes: https://bugzilla.gnome.org/686519

Distrotech/gnome-online-accounts,Distrotech/gnome-online-accounts,dnohales/gnome-online-accounts,ritzk/gnome-online-accounts,halfline/gnome-online-accounts,halfline/gnome-online-accounts,ritzk/gnome-online-accounts,Distrotech/gnome-online-accounts,halfline/gnome-online-accounts,felipeborges/gnome-online-accounts,dnohales/gnome-online-accounts,ritzk/gnome-online-accounts,felipeborges/gnome-online-accounts,felipeborges/gnome-online-accounts,dnohales/gnome-online-accounts