Do not filter out duplicate completions on non-Windows systems.

[JamesWTruher]

It is very likely that native applications will have parameters which differ only by case.
This PR provides a way to get these completions on the platforms where they will likely be found.

PR Summary

PR Checklist

• PR has a meaningful title
  • Use the present tense and imperative mood when describing your changes
• Summarized changes
• Make sure you've added one or more new tests
• Make sure you've tested these changes in terminals that PowerShell is commonly used in (i.e. conhost.exe, Windows Terminal, Visual Studio Code Integrated Terminal, etc.)
• User-facing changes
  • Not Applicable
  • OR
  • Documentation needed at PowerShell-Docs
    • Doc Issue filed:

Microsoft Reviewers: Open in CodeFlow

[daxian-dbw]

LGTM