remove auto-explain-config deprecation warning

activerecord/CHANGELOG.md

+*   Remove deprecation warning for `auto_explain_threshold_in_seconds`.
+
+    *Yves Senn*
+
 *   Remove deprecated `:distinct` option from `Relation#count`.
 
     *Yves Senn*

activerecord/lib/active_record/railtie.rb

@@ -135,17 +135,6 @@ class Railtie < Rails::Railtie # :nodoc:
             EOF
           end
 
-          unless app.config.active_record.delete(:auto_explain_threshold_in_seconds).nil?
-            ActiveSupport::Deprecation.warn <<-EOF.strip_heredoc, []
-              The Active Record auto explain feature has been removed.
-
-              To disable this message remove the `active_record.auto_explain_threshold_in_seconds`
-              option from the `config/environments/*.rb` config file.
-
-              See http://guides.rubyonrails.org/4_0_release_notes.html for more information.
-            EOF
-          end
-
           unless app.config.active_record.delete(:observers).nil?
             ActiveSupport::Deprecation.warn <<-EOF.strip_heredoc, []
               Active Record Observers has been extracted out of Rails into a gem.