The ztypes_windows* file names indicate that these are auto-generated
but they aren't. Rename them to types_windows* to avoid this confusion.

This follows CL 52950 which did the same for golang.org/x/sys.

Change-Id: Ia557ec5d4bcfb6bae20e34e71b5f3f190285794f
Reviewed-on: https://go-review.googlesource.com/75390
Run-TryBot: Tobias Klauser <tobias.klauser@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>