Cleanup source build teams

[MichaelSimons]

Problem: The source-build-internal team is poorly named. It is comprised of the MSFT SB team members. We use it as "the" way to ping the SB team to get help or review SB related topics.

Misconception: The "internal" part is confusing. I field questions along the lines of "what team should we use?" they even often state that they have seen our documentation that says use source-build-internal but didn't think it was right. Folks are using source-build-contrib because it "feels" more appropriate. All 4 active mentions of source-build-contrib should have used source-build-internal

Recommendation: "Rename" the team to source-build. Update all documentation and references to the new team. Post announcements (internally and externally) to notify of the name change. The source-build-contrib team should be deleted.

Implementation:

When a GitHub team is renamed, all existing references must be updated manually. Because of this, a new source-build team should be created, update all documentation and CODEOWNER references to the new team, then delete the source-build-internal team.

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[dotnet-issue-labeler]

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