Remove duplicated ConnectionHandling extension in AR::Base

Thanks @toretore.
https://github.com/rails/rails/commit/9e4c41c903e8e58721f2c41776a8c60ddba7a0a9#commitcomment-2134706

activerecord/lib/active_record/base.rb

@@ -332,7 +332,6 @@ class Base
     extend Translation
     extend DynamicMatchers
     extend Explain
-    extend ConnectionHandling
 
     include Persistence
     include ReadonlyAttributes