Intent to remove: devel/pthread-stublib

[Benny Siegert <bsiegert%gmail.com@localhost>]

I just stumbled upon devel/pthread-stublib, which is a dependency
(sometimes) of MesaLib. According to its description, it does the following:

"Provide dummy implementations of pthread functions like mutex operations
to enable libraries to be used in both thread-aware and non-threaded
programs.
This is for NetBSD<=2; newer operating systems don't need it."

Given that NetBSD 1.6 is ancient history at this point, I would like to
remove it after the branch. Objections?

-- 
Benny