timeout.rb: unused attribute

* lib/timeout.rb (Timeout::ExitException): remove unused attribute,
  klass.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@44519 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

Author: nobu

lib/timeout.rb

@@ -26,7 +26,7 @@ module Timeout
   class Error < RuntimeError
   end
   class ExitException < ::Exception # :nodoc:
-    attr_reader :klass, :thread
+    attr_reader :thread
 
     def self.catch
       exc = new