Go into the app’s system settings, clear data and reboot.
Another way to launch it in Oreo is going into Location settings (tap and hold the notification bar quick-setting for toggling location), and at the bottom (“Location services”) you’ll find an entry for it.
To delete it, I guess it is enough to clear its data, reboot into TWRP and remove /system/priv-app/UnifiedNlp, /system/etc/permissions/privapp-permissions_microg.xml and /system/addon.d/70-microg.sh.
Alternatively, you could just clear its data, remove the latter file and re-flash your LineageOS ROM.
A clearer way will be always restoing the backup you should have performed before flashing it, though.