We can never hit this, because the indirect GLX dispatch code always
forces a current context and checks that it's non-NULL before calling
into the dispatch table. If it's _not_ null, then _glapi_set_context
will call into the driver, which is responsible for calling
_glapi_set_dispatch to make sure the dispatch table is non-NULL.
Also remove _glapi_set_warning_func and friends, since we can no longer
call them even from dead code.
Reviewed-by: Dave Airlie <airlied@redhat.com>
Signed-off-by: Adam Jackson <ajax@redhat.com>