Use upstream whatsapp again (#809)

vendor/golang.org/x/crypto/poly1305/mac_noasm.go

@@ -0,0 +1,11 @@
+// Copyright 2018 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// +build !amd64 gccgo appengine
+
+package poly1305
+
+type mac struct{ macGeneric }
+
+func newMAC(key *[32]byte) mac { return mac{newMACGeneric(key)} }