Remove Struct#to_h backport

actionpack/lib/action_controller/metal/params_wrapper.rb

@@ -1,7 +1,6 @@
 require 'active_support/core_ext/hash/slice'
 require 'active_support/core_ext/hash/except'
 require 'active_support/core_ext/module/anonymous'
-require 'active_support/core_ext/struct'
 require 'action_dispatch/http/mime_type'
 
 module ActionController

activesupport/lib/active_support/core_ext.rb

@@ -1,3 +1,4 @@
-Dir["#{File.dirname(__FILE__)}/core_ext/*.rb"].each do |path|
+DEPRECATED_FILES = ["#{File.dirname(__FILE__)}/core_ext/struct.rb"]
+(Dir["#{File.dirname(__FILE__)}/core_ext/*.rb"] - DEPRECATED_FILES).each do |path|
   require path
 end

activesupport/lib/active_support/core_ext/struct.rb

@@ -1,6 +1,3 @@
-#  Backport of Struct#to_h from Ruby 2.0
-class Struct # :nodoc:
-  def to_h
-    Hash[members.zip(values)]
-  end
-end unless Struct.instance_methods.include?(:to_h)
+require 'active_support/deprecation'
+
+ActiveSupport::Deprecation.warn("This file is deprecated and will be removed in Rails 5.1 with no replacement.")

activesupport/test/core_ext/struct_test.rb

@@ -1,10 +0,0 @@
-require 'abstract_unit'
-require 'active_support/core_ext/struct'
-
-class StructExt < ActiveSupport::TestCase
-  def test_to_h
-    x = Struct.new(:foo, :bar)
-    z = x.new(1, 2)
-    assert_equal({ foo: 1, bar: 2 }, z.to_h)
-  end
-end