Remove vendor directory and add it to the ignore list

vendor/golang.org/x/sys/unix/endian_little.go

@@ -1,9 +0,0 @@
-// Copyright 2016 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 386 amd64 amd64p32 arm arm64 ppc64le mipsle mips64le
-
-package unix
-
-const isBigEndian = false