No need to deprecate Errors#first

This deprecation is useless since the result is still an Error object
and there is no way to fix the code to remove the deprecation.

Let's just accept as a breaking change.

activemodel/CHANGELOG.md

@@ -37,15 +37,13 @@
     extra parameters, found in the original `details` hash.
 
     The change tries its best at maintaining backward compatibility, however 
-    some edge cases won’t be covered, mainly related to manipulating 
-    `errors.messages` and `errors.details` hashes directly. Moving forward, 
+    some edge cases won’t be covered, like `errors#first` will return `ActiveModel::Error` and manipulating
+    `errors.messages` and `errors.details` hashes directly will have no effect. Moving forward,
     please convert those direct manipulations to use provided API methods instead.
 
     The list of deprecated methods and their planned future behavioral changes at the next major release are:
 
     * `errors#slice!` will be removed.
-    * `errors#first` will return Error object instead.
-    * `errors#last` will return Error object instead.
     * `errors#each` with the `key, value` two-arguments block will stop working, while the `error` single-argument block would return `Error` object.
     * `errors#values` will be removed.
     * `errors#keys` will be removed.

activemodel/lib/active_model/errors.rb

@@ -208,16 +208,6 @@ module ActiveModel
       DeprecationHandlingMessageArray.new(messages_for(attribute), self, attribute)
     end
 
-    def first
-      deprecation_index_access_warning(:first)
-      super
-    end
-
-    def last
-      deprecation_index_access_warning(:last)
-      super
-    end
-
     # Iterates through each error object.
     #
     #   person.errors.add(:name, :too_short, count: 2)
@@ -585,15 +575,6 @@ module ActiveModel
       def deprecation_rename_warning(old_method_name, new_method_name)
         ActiveSupport::Deprecation.warn("ActiveModel::Errors##{old_method_name} is deprecated. Please call ##{new_method_name} instead.")
       end
-
-      def deprecation_index_access_warning(method_name, alternative_message)
-        message = +"ActiveModel::Errors##{method_name} is deprecated. In the next release it would return `Error` object instead."
-        if alternative_message
-          message << "\n\nTo achieve the same use:\n\n  "
-          message << alternative_message
-        end
-        ActiveSupport::Deprecation.warn(message)
-      end
   end
 
   class DeprecationHandlingMessageHash < SimpleDelegator

activemodel/test/cases/errors_test.rb

@@ -63,6 +63,14 @@ class ErrorsTest < ActiveModel::TestCase
     }
   end
 
+  def test_first
+    errors = ActiveModel::Errors.new(Person.new)
+    errors.add(:name, :blank)
+
+    error = errors.first
+    assert_kind_of ActiveModel::Error, error
+  end
+
   def test_dup
     errors = ActiveModel::Errors.new(Person.new)
     errors.add(:name)