Remove additional references to roles

Author: lorenyu

app-rails/app/views/users/registrations/new.html.erb

@@ -12,7 +12,6 @@
   </div>
 
   <%= us_form_with model: @form, url: users_registrations_path, local: true do |f| %>
-    <%= f.hidden_field :role %>
     <%= f.honeypot_field %>
     <%= f.email_field :email %>
 

docs/app-rails/auth.md

@@ -13,7 +13,6 @@ Authentication is the process of verifying the credentials of a user. We use AWS
 
 Authorization is the process of determining whether a user has access to a specific resource. We use [Pundit](https://github.com/varvet/pundit) for authorization.
 
-- User roles are defined in the `user_roles` table
 - Policies (`app/policies`) are created for each model to define who can perform what actions
 - Policies are used in controllers to authorize actions
 - Policies are used in views to show/hide elements based on user permissions