Eliminate pre-built assets during source-build

[eerhardt]

Port of #60315 from release/6.0 to main.

This work eliminates using pre-built NuGet packages during source-build. It's probably easiest to review commit-by-commit.

1. Remove RefOnly dependency versions
   This allows for source-build to replace these versions with source-built versions.
2. Eliminate usages of pre-built packages during source-build
   See commit message for details

[ghost]

Tagging subscribers to this area: @dotnet/runtime-infrastructure
See info in area-owners.md if you want to be subscribed.

Issue Details

---

Port of #60315 from release/6.0 to main.

This work eliminates using pre-built NuGet packages during source-build. It's probably easiest to review commit-by-commit.

1. Remove RefOnly dependency versions
   This allows for source-build to replace these versions with source-built versions.
2. Eliminate usages of pre-built packages during source-build
   See commit message for details

Author:	eerhardt
Assignees:	-
Labels:	area-Infrastructure
Milestone:	-

[ViktorHofer]

For the .NETFramework msbuild tasks, don't we want to build them because prebuilds with them? Last time I spoke with @dseefeld he mentioned that the .NETFramework targeting packs are already available as prebuilds and are OK to be used during source build.

[eerhardt]

For the .NETFramework msbuild tasks, don't we want to build them because prebuilds with them?

Sort of, but not really. The reason I needed to remove the .NET Framework build for the msbuild tasks is because we are now using the "source-built" MSBuild and NuGet packages during our "2nd pass" build. However, when MSBuild and NuGet build for source-build, they only build for netstandard2.0 and net6.0 respectively, not net4x:

https://github.com/dotnet/msbuild/blob/aac64bbabfcea279aa34875563848003887e8c84/src/Directory.Build.props#L29-L30

https://github.com/NuGet/NuGet.Client/blob/3e2fdae24e0d4982188a5a82a0291d6825fffbfc/build/common.project.props#L21-L28

So while you can build a net4x library in source-build, these tasks projects have other dependencies that don't.

Lastly, it isn't strictly "required" to build these tasks for net4x in source-build, so it was easiest to just disable that TFM during the build.