Remove support of pkgproj in TargetFramework.Sdk

[ViktorHofer]

Pkgprojs are removed in the consuming part of dotnet/runtime (libraries) and the TargetFramework.Sdk hence need to support them anymore.

To double check:

• The right tests are in and and the right validation has happened. Guidance: https://github.com/dotnet/core-eng/tree/master/Documentation/Validation

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[ghost]

Apologies, while this PR appears ready to be merged, I've been configured to only merge when all checks have explicitly passed. The following integrations have not reported any progress on their checks and are blocking auto-merge:

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[ghost]

Apologies, while this PR appears ready to be merged, I've been configured to only merge when all checks have explicitly passed. The following integrations have not reported any progress on their checks and are blocking auto-merge:

1. DotNet Maestro - Int
2. Codecov
3. DotNet Maestro
4. Dependabot

These integrations are possibly never going to report a check, and unblocking auto-merge likely requires a human being to update my configuration to exempt these integrations from requiring a passing check.

Give feedback on this

From the bot dev team

We've tried to tune the bot such that it posts a comment like this only when auto-merge is blocked for exceptional, non-intuitive reasons. When the bot's auto-merge capability is properly configured, auto-merge should operate as you would intuitively expect and you should not see any spurious comments.

Please reach out to us at fabricbotservices@microsoft.com to provide feedback if you believe you're seeing this comment appear spuriously. Please note that we usually are unable to update your bot configuration on your team's behalf, but we're happy to help you identify your bot admin.