Change CAPTCHA handling to be only on email verification

This simplifies the implementation considerably, and while not providing
ideal UX, it's the most flexible approach.

app/views/auth/confirmations/captcha.html.haml

@@ -5,7 +5,7 @@
   = hidden_field_tag :confirmation_token, params[:confirmation_token]
 
   .field-group
-    = render_captcha_if_needed
+    = render_captcha
 
   .actions
     %button.button= t('challenge.continue')

app/views/auth/registrations/new.html.haml

@@ -38,9 +38,6 @@
   .fields-group
     = f.input :agreement, as: :boolean, wrapper: :with_label, label: whitelist_mode? ? t('auth.checkbox_agreement_without_rules_html', terms_path: terms_path) : t('auth.checkbox_agreement_html', rules_path: about_more_path, terms_path: terms_path), required: true
 
-  .field-group
-    = render_captcha_if_needed
-
   .actions
     = f.button :button, @invite.present? ? t('auth.register') : sign_up_message, type: :submit