If a Google button signup fallbacks because of username don't force to validate email

[juanignaciosl]

See #3902. If you try to signup in a organization with google and username is taken you are forced to validate your email, but it shouldn't be needed.

Steps (change username with a username of a Google account you own):

1. New incognito window. Create a "username", "username@non-google-domain.com" user.
2. New incognito window. Try to do a sigup with "username@google-domain.com". Since username is taken you're prompted with the fallback screen asking you for a new username. Create the user. User is created but you must "check your email and activate your account". Since you can sign up with your google account that should not be necessary.