Remove obsolete new_session helper

After #44748, the `new_session` helper no longer takes a block and is
the same as calling `app(true)`. Therefore, I think there's no reason to
expose it to Rails console users.

railties/lib/rails/commands/console/irb_console.rb

@@ -27,28 +27,25 @@ def execute
       end
     end
 
-    class NewSession < RailsHelperBase
-      description "Creates a new ActionDispatch::Integration::Session. If a block is given, the new session will be yielded to it."
-
-      def execute(*)
-        app = Rails.application
-        session = ActionDispatch::Integration::Session.new(app)
-
-        # This makes app.url_for and app.foo_path available in the console
-        session.extend(app.routes.url_helpers)
-        session.extend(app.routes.mounted_helpers)
-
-        session
-      end
-    end
-
-    class AppInstance < NewSession
+    class AppInstance < RailsHelperBase
       description "Creates a new ActionDispatch::Integration::Session and memoizes it. Use `app(true)` to create a new instance."
 
       def execute(create = false)
         @app_integration_instance = nil if create
-        @app_integration_instance ||= super
+        @app_integration_instance ||= new_session
       end
+
+      private
+        def new_session
+          app = Rails.application
+          session = ActionDispatch::Integration::Session.new(app)
+
+          # This makes app.url_for and app.foo_path available in the console
+          session.extend(app.routes.url_helpers)
+          session.extend(app.routes.mounted_helpers)
+
+          session
+        end
     end
 
     class Reloader < IRB::Command::Base
@@ -65,7 +62,6 @@ def execute(*)
 
     IRB::HelperMethod.register(:helper, ControllerHelper)
     IRB::HelperMethod.register(:controller, ControllerInstance)
-    IRB::HelperMethod.register(:new_session, NewSession)
     IRB::HelperMethod.register(:app, AppInstance)
     IRB::Command.register(:reload!, Reloader)
 

railties/test/application/console_test.rb

@@ -168,12 +168,6 @@ def test_controller_helper_method
     write_prompt "controller.class.name", "ApplicationController"
   end
 
-  def test_new_session_helper_method
-    spawn_console("-e development")
-
-    write_prompt "new_session.class.name", "ActionDispatch::Integration::Session"
-  end
-
   def test_app_helper_method
     app_file "config/routes.rb", <<-RUBY
       Rails.application.routes.draw do