Remove unnecessary fixme on new thread stack size
As the FIXME itself notes, there's nothing to fix here.
And as the documentation for [`CreateThread`] says of `dwStackSize`, the value is rounded up to the nearest page. A 4kb stack is very small but perfectly usable if you're careful. Of course it will be very limited but there's no reason to add artificial limits. We don't know what the user is doing.
[`CreateThread`]: https://learn.microsoft.com/en-us/windows/win32/api/processthreadsapi/nf-processthreadsapi-createthread
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