According to the man page, the contents of that file should have been copied to /run/resolvconf/resolv.conf. If you are going to use resolveconf, I would suggest reading its instructions and determining why it isn’t generating the configuration you’re after rather than fighting against it.
Note also that newer versions of Ubuntu, the default resolver configuration will send requests to systemd-resolved. So another option would be to leave resolv.conf as is and edit the systemd-resolved configuration file at /etc/systemd/resolve.conf.