Revert "Delete vendor/ and the route proxy's: the build module fetches the modules, the root image builds with -mod=mod (issue 1305, C6)"

This reverts commit 9c4bf1f08b.

vendor/github.com/klauspost/compress/s2/decode_asm.go

@@ -0,0 +1,17 @@
+// Copyright 2016 The Snappy-Go Authors. All rights reserved.
+// Copyright (c) 2019 Klaus Post. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+//go:build (amd64 || arm64) && !appengine && gc && !noasm
+// +build amd64 arm64
+// +build !appengine
+// +build gc
+// +build !noasm
+
+package s2
+
+// decode has the same semantics as in decode_other.go.
+//
+//go:noescape
+func s2Decode(dst, src []byte) int