mesa: remove MESA_GLSL=no_opts env option

mesa: remove MESA_GLSL=no_opts env option

This is confusing because is only applys to GL_ARB_vertex/fragment_program,
and because of that its also not very useful.

If someone requires this for debugging they can just make an ad-hoc
code change.

Reviewed-by: Brian Paul <brianp@vmware.com>
Reviewed-by: Nicolai Hähnle <nicolai.haehnle@amd.com>
Reviewed-by: Marek Olšák <marek.olsak@amd.com>