Drop Application#scopes generator and warning

It was introduced for upgrading from v2 to v3. It's not necessary in v4
and up.

NEWS.md

@@ -5,6 +5,8 @@ User-visible changes worth mentioning.
 - [#823] Make configuration and specs ORM independent
 - [#777] Add support for public client in password grant flow
 - [#745] Add created_at timestamp to token generation options
+- [#838] Drop `Application#scopes` generator and warning, introduced for
+  upgrading doorkeeper from v2 to v3.
 
 ---
 

lib/doorkeeper/config.rb

@@ -10,17 +10,12 @@ def self.configure(&block)
     setup_orm_adapter
     setup_orm_models
     setup_application_owner if @config.enable_application_owner?
-    check_requirements
   end
 
   def self.configuration
     @config || (fail MissingConfiguration)
   end
 
-  def self.check_requirements
-    @orm_adapter.check_requirements!(configuration)
-  end
-
   def self.setup_orm_adapter
     @orm_adapter = "doorkeeper/orm/#{configuration.orm}".classify.constantize
   rescue NameError => e

lib/doorkeeper/orm/active_record.rb

@@ -18,22 +18,6 @@ def self.initialize_application_owner!
 
         Doorkeeper::Application.send :include, Doorkeeper::Models::Ownership
       end
-
-      def self.check_requirements!(_config)
-        if ::ActiveRecord::Base.connected? &&
-           ::ActiveRecord::Base.connection.table_exists?(
-             Doorkeeper::Application.table_name
-           )
-          unless Doorkeeper::Application.column_names.include?("scopes")
-            migration_path = '../../../generators/doorkeeper/templates/add_scopes_to_oauth_applications.rb'
-            puts <<-MSG.squish
-[doorkeeper] Missing column: `oauth_applications.scopes`.
-Create the following migration and run `rake db:migrate`.
-            MSG
-            puts File.read(File.expand_path(migration_path, __FILE__))
-          end
-        end
-      end
     end
   end
 end