Remove deprecated default_charset= from AC::Base

This should be set globally as a configuration, using
`config.action_dispatch.default_charset` instead

actionpack/lib/action_controller/metal/compatibility.rb

@@ -4,10 +4,6 @@ module Compatibility
 
     # Temporary hax
     included do
-      class << self
-        delegate :default_charset=, :to => "ActionDispatch::Response"
-      end
-
       self.protected_instance_variables = [
         :@_status, :@_headers, :@_params, :@_env, :@_response, :@_request,
         :@_view_runtime, :@_stream, :@_url_options, :@_action_has_layout

actionpack/lib/action_dispatch/railtie.rb

@@ -11,6 +11,7 @@ class Railtie < Rails::Railtie
     config.action_dispatch.ignore_accept_header = false
     config.action_dispatch.rescue_templates = { }
     config.action_dispatch.rescue_responses = { }
+    config.action_dispatch.default_charset = nil
 
     config.action_dispatch.rack_cache = {
       :metastore => "rails:/",
@@ -21,7 +22,7 @@ class Railtie < Rails::Railtie
     initializer "action_dispatch.configure" do |app|
       ActionDispatch::Http::URL.tld_length = app.config.action_dispatch.tld_length
       ActionDispatch::Request.ignore_accept_header = app.config.action_dispatch.ignore_accept_header
-      ActionDispatch::Response.default_charset = app.config.encoding
+      ActionDispatch::Response.default_charset = app.config.action_dispatch.default_charset || app.config.encoding
 
       ActionDispatch::ExceptionWrapper.rescue_responses.merge!(config.action_dispatch.rescue_responses)
       ActionDispatch::ExceptionWrapper.rescue_templates.merge!(config.action_dispatch.rescue_templates)

actionpack/test/controller/content_type_test.rb

@@ -68,12 +68,12 @@ def test_render_defaults
   end
 
   def test_render_changed_charset_default
-    OldContentTypeController.default_charset = "utf-16"
+    ActionDispatch::Response.default_charset = "utf-16"
     get :render_defaults
     assert_equal "utf-16", @response.charset
     assert_equal Mime::HTML, @response.content_type
   ensure
-    OldContentTypeController.default_charset = "utf-8"
+    ActionDispatch::Response.default_charset = "utf-8"
   end
 
   # :ported:
@@ -105,12 +105,12 @@ def test_nil_charset_from_body
   end
 
   def test_nil_default_for_erb
-    OldContentTypeController.default_charset = nil
+    ActionDispatch::Response.default_charset = nil
     get :render_default_for_erb
     assert_equal Mime::HTML, @response.content_type
     assert_nil @response.charset, @response.headers.inspect
   ensure
-    OldContentTypeController.default_charset = "utf-8"
+    ActionDispatch::Response.default_charset = "utf-8"
   end
 
   def test_default_for_erb

railties/test/application/configuration_test.rb

@@ -287,6 +287,14 @@ def index
       assert_equal Rails.application, ActionDispatch.test_app
     end
 
+    test "sets ActionDispatch::Response.default_charset" do
+      make_basic_app do |app|
+        app.config.action_dispatch.default_charset = "utf-16"
+      end
+
+      assert_equal "utf-16", ActionDispatch::Response.default_charset
+    end
+
     test "sets all Active Record models to whitelist all attributes by default" do
       add_to_config <<-RUBY
         config.active_record.whitelist_attributes = true