Get rid of the authHook parameter on processConnection

This is (morally) dead code.

As @edolstra pointed out in
https://github.com/NixOS/nix/pull/5226#discussion_r1073470813, this is
no longer needed.

I created this in 8d4162ff9e, so it is
fitting that I now destroy it :).

src/libstore/build/local-derivation-goal.cc

@@ -1516,8 +1516,7 @@ void LocalDerivationGoal::startDaemon()
                 FdSink to(remote.get());
                 try {
                     daemon::processConnection(store, from, to,
-                        daemon::NotTrusted, daemon::Recursive,
-                        [&](Store & store) {});
+                        daemon::NotTrusted, daemon::Recursive);
                     debug("terminated daemon connection");
                 } catch (SysError &) {
                     ignoreException();