title: Remove Devise Flash Notices for Sign out
body: <p>As the name says, I am using devise for user auth in a rails 3 app
  Upon user log out, there is a flash notice, "User Successfully signed out" that I don't want to appear. However, I can't figure out how to remove the notice. </p>
  
  <p>Is there a way to get around just making it blank? I would like to completely remove the notice so that, ideally, there's not even an html div for notice</p>