msi: Put the uninstall key for 32-bit packages under Wow6432Node on 64-bit.

[Hans Leidekker]

On Tue, 2010-10-05 at 16:59 +0200, testbot at testbot.winehq.org wrote:

> While running your changed tests on Windows, I think I found new failures.
> Being a bot and all I'm not very good at pattern recognition, so I might be
> wrong, but could you please double-check?
> Full results can be found at
> http://testbot.winehq.org/JobDetails.pl?Key=5824
> 
> Your paranoid android.
> 
> 
> === W7PROX64 (64 bit install) ===
> install.c:10427: Test failed: key not created

This failure existed before my patch.