Remove unused line

Removed `self.value = value` in TimerTask#timeout_task
This line was probably added as a copy-mistake from the above
method (execute_task).

Author: fzakaria

lib/concurrent-ruby/concurrent/timer_task.rb

@@ -325,7 +325,6 @@ def execute_task(completion)
     def timeout_task(completion)
       return unless @running.true?
       if completion.try?
-        self.value = value
         schedule_next_task
         observers.notify_observers(Time.now, nil, Concurrent::TimeoutError.new)
       end