wpa-supplicant: rename bbappend to match oe-core

Signed-off-by: Martin Jansa <Martin.Jansa@gmail.com>
meta-systemd: remove wpa-supplicant bbappend

* oe-core now has wpa-supplicant 2.0, but also installs wpa_supplicant.service to PN
* feel free to add new bbappend with only systemd inherit and updated SYSTEMD_PACKAGES

Signed-off-by: Martin Jansa <Martin.Jansa@gmail.com>