Upstream Go tricks Windows into enabling long path support by setting an undocumented flag in the PEB. The Microsoft Go fork can't use undocumented APIs, so this commit removes the hack.

There is no documented way to enable long path support from within the process, so this this is a breaking change for the Microsoft Go fork. Note that the Go standard library makes a best effort to support long paths by using the `\\?\` prefix when possible, so this change should only affect long relative paths, which can't be used with the `\\?\`.

lol?