not sure what you exactly looking for.
Volumio already boots up headless, you only get a GUI when you actively install a plugin for it.
So, unless you need to work with the volumio system, booting the way it does currently should be OK for you.
No need to remove or re-configure anything.
You access volumio via any web client on your network (PC, smartphone, tablet), just enter “http://volumio.local” in its browser.
This usually works, but depends a little on your network. In case it doesn’t, enter “http://<put-volumio’s-ip-here>” (without the ‘<’ and ‘>’).