network: remove `wpa-none` from `key_mgmt`

Network Manager dropped wpa-none value from key_mgmt a while ago[0] There is no need to test for this option anymore.

[0]https://gitlab.freedesktop.org/NetworkManager/NetworkManager/-/commit/c97e0ce30b8b9b118d47d0e02e6ebe7556e9f0c4