meson: drop unused system-pybind11 option
meson: drop unused system-pybind11 option

system-pybind11 is no longer used and can be removed.

Signed-off-by: Tomi Valkeinen <e1ca4dbb8be1acaf20734fecd2da10ed1d46a9bb@ideasonboard.com>

tomba/kmsxx,tomba/kmsxx,tomba/kmsxx,tomba/kmsxx