Fix Devise Turbo Stream responses for flash messages

Wire Users::DeviseController as Devise parent controller with the
Turbo-aware responder, so failed form submissions (login, password
reset) render correctly as HTML with 422 status instead of
unprocessable turbo-stream content that Turbo silently drops.

Also fixes a NameError in the responder (rendering_options ->
error_rendering_options) and removes the dead TurboController.

app/controllers/turbo_controller.rb

@@ -1,18 +0,0 @@
-class TurboController < ApplicationController
-  class Responder < ActionController::Responder
-    def to_turbo_stream
-      controller.render(options.merge(formats: :html))
-    rescue ActionView::MissingTemplate => error
-      if get?
-        raise error
-      elsif has_errors? && default_action
-        render rendering_options.merge(formats: :html, status: :unprocessable_entity)
-      else
-        redirect_to navigation_location
-      end
-    end
-  end
-
-  self.responder = Responder
-  respond_to :html, :turbo_stream
-end

app/controllers/users/devise_controller.rb

@@ -6,7 +6,7 @@ class Users::DeviseController < ApplicationController
       if get?
         raise error
       elsif has_errors? && default_action
-        render rendering_options.merge(formats: :html, status: :unprocessable_entity)
+        render error_rendering_options.merge(formats: :html, status: :unprocessable_entity)
       else
         redirect_to navigation_location
       end