version: delete GENERATE.go.

It existed previously to persuade Go that redo-ful directory was
a Go package prior to the first build. But now we have other Go
files in the directory that will fulfil that function.

Signed-off-by: David Anderson <danderson@tailscale.com>

version/GENERATE.go

@@ -1,8 +0,0 @@
-// Copyright (c) 2020 Tailscale Inc & AUTHORS All rights reserved.
-// Use of this source code is governed by a BSD-style
-// license that can be found in the LICENSE file.
-
-// Placeholder that indicates this directory is a valid go package,
-// but that redo must 'redo all' in this directory before it can
-// be imported.
-package version