[release7.0] Reconcile stable versioning

[crummel]

Follow-up on #3118:

• Bootstrapping expects to have the unstable versions of certain runtime packages available
• The installer build expects to have stable versions of certain other runtime packages available
• However we can't currently version some runtime packages unstably and other stably.
  • We should be able to just drop our stable version manipulation but that didn't work in a first pass.
• Also remove the workaround added once the permanent fix is in.
• This problem does not repro in the .NET 8.0 VMR prototype nor the release/6.0 branch so release/7.0 is the only required target branch.

I couldn't figure out the best area label to add to this issue. If you have write-permissions please help me learn by adding exactly one area label.

[crummel]

release/7.0 PR: dotnet/installer#15121

[crummel]

Main port PR: dotnet/installer#15467