The go.dev front page download button changes what links to
based on JS: if this is a Mac, it links to the darwin/amd64 pkg.
Otherwise it links to the windows/amd64 msi.

This is obviously wrong on all non-Mac, non-Windows systems,
such as Linux, FreeBSD, phones, tablets, and so on.
None of them want the Windows MSI.

It is also less obviously wrong on all arm64 Mac and Windows systems,
of which there will be more and more.

Changing whether the button downloads a file or goes to a new page
based on browser properties also makes it very difficult to write
documentation about how to install Go, since "click Download"
does different things for different people.

It's also very difficult to tell what architecture the browser is, by design.
So our chance of linking to the right download is going to plummet as
arm64-based systems proliferate.

Instead, just link to the download page and let people find what they need.

Fixes golang/go#49765.

Change-Id: I0761fddffaef3a36087fd050ae276111339ea2dc
Reviewed-on: https://go-review.googlesource.com/c/website/+/366976
Trust: Russ Cox <rsc@golang.org>
Run-TryBot: Russ Cox <rsc@golang.org>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Jamal Carvalho <jamal@golang.org>