libvhost-user: drop dependency on glib

libvhost-user is meant to be free of glib dependency. Make sure it is
by droping qemu/osdep.h (which included glib.h)

This fixes a bad malloc()/g_free() pair.

Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>