fix: remove PowerShell from Windows registry interactions

[rbtr]

Reason for Change: PowerShell is heavy (+30mb of memory footprint per invocation). We don't need to use it to interact with the Windows Registry (or ServiceManager) - the Go stdlib has good native bindings that should use instead.

Notes: This functionality was introduced in #1306. In #2315, it was changed to conditionally set the reg key value only if the HNS path exists. Why? It seems simpler and harmless to always try to set the reg key, so that's what I have done. Unclear if this is problematic - cc @ZetaoZhuang

Supersedes and closes #2974 and #2961 (and #2949)