Remove deprecated Devise.activerecord51? method

CHANGELOG.md

@@ -8,6 +8,7 @@
   * Remove deprecated `scope` second argument from `sign_in(resource, :admin)` controller test helper, use `sign_in(resource, scope: :admin)` instead. [#5803](https://github.com/heartcombo/devise/pull/5803)
   * Remove deprecated `Devise::TestHelpers`, use `Devise::Test::ControllerHelpers` instead. [#5803](https://github.com/heartcombo/devise/pull/5803)
   * Remove deprecated `Devise::Models::Authenticatable::BLACKLIST_FOR_SERIALIZATION` [#5598](https://github.com/heartcombo/devise/pull/5598)
+  * Remove deprecated `Devise.activerecord51?` method.
   * Remove `SecretKeyFinder` and use `app.secret_key_base` as the default secret key for `Devise.secret_key` if a custom `Devise.secret_key` is not provided.
 
     This is potentially a breaking change because Devise previously used the following order to find a secret key:

lib/devise.rb

@@ -524,14 +524,6 @@ module Devise
   def self.deprecator
     @deprecator ||= ActiveSupport::Deprecation.new("5.0", "Devise")
   end
-
-  def self.activerecord51? # :nodoc:
-    deprecator.warn <<-DEPRECATION.strip_heredoc
-      [Devise] `Devise.activerecord51?` is deprecated and will be removed in the next major version.
-      It is a non-public method that's no longer used internally, but that other libraries have been relying on.
-    DEPRECATION
-    defined?(ActiveRecord) && ActiveRecord.gem_version >= Gem::Version.new("5.1.x")
-  end
 end
 
 require 'warden'

test/devise_test.rb

@@ -111,10 +111,4 @@ class DeviseTest < ActiveSupport::TestCase
       assert_no_match Devise.email_regexp, email
     end
   end
-
-  test 'Devise.activerecord51? deprecation' do
-    assert_deprecated("`Devise.activerecord51?` is deprecated", Devise.deprecator) do
-      Devise.activerecord51?
-    end
-  end
 end