cmd/dist: remove special test timeout scale for Windows

cmd/dist: remove special test timeout scale for Windows

In https://golang.org/cl/33804 I screwed up a GOOS == "windows"
check into a bogus comparison against GOARCH == "windows".

But turns out the builders are happy anyway, so remove the windows
special case.

Change-Id: I820b1d49d5b3e8cbffe4516fc39f514326dc39f8
Reviewed-on: https://go-review.googlesource.com/33893
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Minux Ma <minux@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>