Remove manifest exclusion for Mono, Shortstack verticals from join-verticals.proj

[akoeplinger]

This is sort of related to #4648

Because multiple non-primary verticals are producing the same assets a workaround was added to exclude Mono/Shortstack:
https://github.com/dotnet/sdk/blob/bdae92e56e504adcbba6f3d9eda3dccfd4158934/src/SourceBuild/content/eng/join-verticals.proj#L24

But this causes e.g. Mono runtime packs or NativeAOT runtime packs for maccatalyst-x64 to be excluded in the final join, even though these are only produced in one vertical.