I have the stock lxd 3.0.3 from apt-get (bionic). Can I uninstall lxcfs.service?
apt-cache show lxd (depends section) should give you a hint that this is not a good idea.
Indeed, the deb does depend on lxcfs so you can’t remove the package.
Disabling the lxcfs service should be fine, though obviously all LXD containers will then show the host values for all the resources values in the various proc files.