Remove deprecated methods re: serialized attributes

These methods were deprecated in PT 5.0.0
https://github.com/airblade/paper_trail/pull/679

CHANGELOG.md

@@ -9,6 +9,10 @@ recommendations of [keepachangelog.com](http://keepachangelog.com/).
 
 - Drop support for ruby 1.9.3, whose EOL was 2015-02-23
 - Drop support for ruby 2.0.0, whose EOL was 2016-02-24
+- Remove deprecated config methods:
+  - PaperTrail.serialized_attributes?
+  - PaperTrail.config.serialized_attributes
+  - PaperTrail.config.serialized_attributes=
 
 ### Added
 

lib/paper_trail.rb

@@ -34,14 +34,6 @@ module PaperTrail
       !!PaperTrail.config.enabled
     end
 
-    def serialized_attributes?
-      ActiveSupport::Deprecation.warn(
-        "PaperTrail.serialized_attributes? is deprecated without replacement " +
-          "and always returns false."
-      )
-      false
-    end
-
     # Sets whether PaperTrail is enabled or disabled for the current request.
     # @api public
     def enabled_for_controller=(value)

lib/paper_trail/config.rb

@@ -18,21 +18,6 @@ module PaperTrail
       @serializer = PaperTrail::Serializers::YAML
     end
 
-    def serialized_attributes
-      ActiveSupport::Deprecation.warn(
-        "PaperTrail.config.serialized_attributes is deprecated without " +
-          "replacement and always returns false."
-      )
-      false
-    end
-
-    def serialized_attributes=(_)
-      ActiveSupport::Deprecation.warn(
-        "PaperTrail.config.serialized_attributes= is deprecated without " +
-          "replacement and no longer has any effect."
-      )
-    end
-
     # Previously, we checked `PaperTrail::VersionAssociation.table_exists?`
     # here, but that proved to be problematic in situations when the database
     # connection had not been established, or when the database does not exist

lib/paper_trail/model_config.rb

@@ -80,6 +80,10 @@ module PaperTrail
       options[:on] = Array(options[:on]) # Support single symbol
       @model_class.send :include, ::PaperTrail::Model::InstanceMethods
       if ::ActiveRecord::VERSION::STRING < "4.2"
+        ::ActiveSupport::Deprecation.warn(
+          "Your version of ActiveRecord (< 4.2) has reached EOL. PaperTrail " \
+          "will soon drop support. Please upgrade ActiveRecord ASAP."
+        )
         @model_class.send :extend, AttributeSerializers::LegacyActiveRecordShim
       end
       setup_options(options)