We were writing the same code twice, with the only difference being the
text "Sign up" in the sign_up action, and "Sign in" in the sign_in
action.
Note we're renaming the `omniauth.info_*` I18n keys so we don't need to
add new exceptions to the `ignore_unused` list, and so it's consistent
with all the other keys under the `omniauth` key.
ed2b217a08