remove unnecessary LRU for internode auth token (#20119)

removes contentious usage of mutexes in LRU, which
were never really reused in any manner; we do not
need it.

To trust hosts, the correct way is TLS certs; this PR completely
removes this dependency, which has never been useful.

```
0  0%  100%  25.83s 26.76%  github.com/hashicorp/golang-lru/v2/expirable.(*LRU[...])
0  0%  100%  28.03s 29.04%  github.com/hashicorp/golang-lru/v2/expirable.(*LRU[...])
```

Bonus: use `x-minio-time` as a nanosecond to avoid unnecessary
parsing logic of time strings instead of using a more
straightforward mechanism.

cmd/common-main.go

@@ -871,6 +871,12 @@ func loadRootCredentials() {
 	} else {
 		globalActiveCred = auth.DefaultCredentials
 	}
+
+	var err error
+	globalNodeAuthToken, err = authenticateNode(globalActiveCred.AccessKey, globalActiveCred.SecretKey)
+	if err != nil {
+		logger.Fatal(err, "Unable to generate internode credentials")
+	}
 }
 
 // Initialize KMS global variable after valiadating and loading the configuration.