Remove two unnecessary .NET Standard 1.x dependencies.

[teo-tsirpanis]

Fix Issue N/A.

Changes

System.Diagnostics.StackTrace and TraceSource are not needed in projects that target .NET Standard 2.0. Referencing them substantially increases the transitive dependencies.

Checklist

• I ran Unit Tests locally. - couldn't because I was getting errors CS7034 - seem unrelated to my change
• CHANGELOG.md updated with one line description of the fix, and a link to the original issue if available.

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• Design discussion issue #
• Changes in public surface reviewed

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[TimothyMothra]

@teo-tsirpanis Thank you!