VS: Revert "Add missing label in C# project-build events"

Brad Kingrequested to merge
brad.king/cmake:vs-csproj-scripts into master

Revert !6485 (merged). The change broke cases using multiple successful custom commands. Revert it pending further investigation into the interaction of the generated script code with Microsoft.Common.CurrentVersion.targets, and whether this is needed for all managed projects or just C# projects.

Also add a test covering the case that was broken.

Fixes: #22964 (closed)
Issue: #21440 (closed)
Backport: release

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