all: Use own automaxprocs package that doesn't log (ref #9436) (#9437)

### Purpose

🤫

lib/automaxprocs/automaxprocs.go

@@ -0,0 +1,15 @@
+// Copyright (C) 2024 The Syncthing Authors.
+//
+// This Source Code Form is subject to the terms of the Mozilla Public
+// License, v. 2.0. If a copy of the MPL was not distributed with this file,
+// You can obtain one at https://mozilla.org/MPL/2.0/.
+
+package automaxprocs
+
+import (
+	"go.uber.org/automaxprocs/maxprocs"
+)
+
+func init() {
+	maxprocs.Set()
+}