Relays typically don't need a ControlPort or ControlSocket.
That said, having one that is only available on localhost (or via the
local filesystem with proper permissions) isn't really a problem.
If you really don't want that ControlSocket and you're using something
similar to Debian, it is getting set in
/usr/share/tor/tor-service-defaults-torrc. Comment it out there and
reload tor.
Warning: that these files in /usr/share/tor aren't supposed to be
edited, and if the tor package ever has an update that changes them, the
update will be less smooth (e.g. it will refuse to work
non-interactively, or it may clobber your changes).