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/daemon.cc

@@ -985,8 +985,7 @@ void processConnection(
     FdSource & from,
     FdSink & to,
     TrustedFlag trusted,
-    RecursiveFlag recursive,
-    std::function<void(Store &)> authHook)
+    RecursiveFlag recursive)
 {
     auto monitor = !recursive ? std::make_unique<MonitorFdHup>(from.fd) : nullptr;
 
@@ -1029,10 +1028,6 @@ void processConnection(
 
     try {
 
-        /* If we can't accept clientVersion, then throw an error
-           *here* (not above). */
-        authHook(*store);
-
         tunnelLogger->stopWork();
         to.flush();