mesaglut

mesaglut (libglut.*)'s development has been stalled for most of the
decade, with work having entirely moved to the freeglut fork. it doesn't
have any users in src or pkgsrc any more so is mostly hanging around
doing nothing (there are no users in src, and i switched everything in
pkgsrc to use freeglut a while ago).

if i was to make it no longer build as part of the X sets would it be
stepping on anyone's toes? there might be a slim chance someone built
a bespoke application on top of this library for netbsd, but i think
it's more likely it was included because it used to be developed as a
mesa component and no longer is.

but then, do we want freeglut in xsrc? it should be a drop-in replacement
but i suspect nobody cares. it's another library for making using opengl
platform neutral and there's a bunch of more popular ones to choose from
(sdl, glfw, allegro, etc)