I think Pedro will need more information. I'm not quite sure what you are asking for.
Regardless of what you remove or make smaller on the message header bar people can always manage to write longer subject lines than space allows on their particular screen (as I have attempted to do on this post).
What do you want to happen with a long subject line?
What do you want to do when someone views even your short subject in a window that is so narrow the subject disappears?
Volunteer Helper - but recommending that users move off the platform!
Once the admin for GregHelp now deleted.