Remove left-overs from assembly signing

[bart-vmware]

Description

This PR removes non-working left-overs from the codebase, related to assembly signing (which is not to be confused with NuGet package signing). As explained at #18 (comment), there's no benefit it trying to pursue this on .NET Core and later versions.

Fixes #18.

Quality checklist

• Your code complies with our Coding Style.
• You've updated unit and/or integration tests for your change, where applicable.
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• You've added required license files and/or file headers (explaining where the code came from with proper attribution), where code is copied from StackOverflow, a blog, or OSS.

[bart-vmware]

/azp run Steeltoe.All

[azure-pipelines]

Azure Pipelines successfully started running 1 pipeline(s).

[sonarqubecloud]

Kudos, SonarCloud Quality Gate passed!   

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[TimHess]

LGTM