Remove .NET 8 upgrade RID workaround after the next Dev Home SDK upgrade

[agniuks]

As Manodasan Wignarajah (@manodasanW) figured out, the use of version-specific RIDs and the associated workaround will no longer be needed once there's a new version of the Dev Home SDK and the extensions upgrade to it. Namely it needs this change here: Blaming devhome/extensionsdk/nuget/Microsoft.Windows.DevHome.SDK.nuspec at c08f7ed23e6e0070a6d5ab24e40c257309f27a75 · microsoft/devhome (github.com).

Originally posted by @AgneLukoseviciute in microsoft/DevHomeAzureExtension#121 (comment)

The work here is to remove the workaround at the bottom of Directory.Build.props and removing windows versions from the Runtime Identifiers.

GitHub Extension equivalent to: microsoft/DevHomeAzureExtension#81