specs: Remove GLX_RENDERER_ID_MESA from GLX_MESA_query_renderer

specs: Remove GLX_RENDERER_ID_MESA from GLX_MESA_query_renderer

This has not even had an attempt at implementation. If you asked for
renderer 0 - which, the spec implies, should always work - then
dri2_convert_glx_attribs would fail, we'd silently fall back to creating
an indirect context, and xserver would also not recognize the attribute
and would throw BadValue at you.

The API would be difficult to use in any case, since there's no way to
enumerate how many renderers the screen has. I'd be tempted to add that
by defining:

    glXQueryRendererIntegerMESA(dpy, screen,
                                /* renderer = */ -1,
                                0, &value);

to return the number of renderers, but a new entrypoint might be
cleaner. Still, better to not specify it at all than to lie about it.

Reviewed-by: Emil Velikov <emil.velikov@collabora.com>
Signed-off-by: Adam Jackson <ajax@redhat.com>