Remove _OverrideArcadeInitializeBuildToolFramework env var

[ViktorHofer]

https://github.com/dotnet/sdk/blob/f542dd4ea220971012db09c80b8e86016210e95d/src/SourceBuild/content/repo-projects/Directory.Build.props#L141C36-L141C79

Since dotnet/arcade@e0270d6, we don't need to tell the build scripts anymore which TFM Arcade built for. The TFM isn't part of the package path anymore.

Therefore, after a re-bootstrap with an updated Arcade SDK we should be able to remove the _OverrideArcadeInitializeBuildToolFramework.

[dotnet-issue-labeler]

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[dotnet-issue-labeler]

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[ViktorHofer]

Fixed with dotnet/sdk@0d4182f