Remove unused using statements and sort them

[bergmeister]

PR Summary

Remove unused using statements and sort them via the Remove and sort usings feature in Visual Studio, which also fixes the indentation of #if pragmas as well.
This reduces vertical scrolling and makes the using statements more readable because there are less and the are sorted alphabetically.

PR Checklist

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• [NA] Make sure you've added a new test if existing tests do not effectively test the code changed
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[JamesWTruher]

nice!