Remove usings from templates implicitly added by the SDK (#34219)

-Depends on dotnet/sdk#18459 flowing to dotnet/aspnetcore repo before we can merge this
- There's a couple of places we could remove usings from .razor files but need to verify the global usings flow into Razor compiler (#34217)
- Reordered usings in some places to ensure they get emitted in alphabetical order (modulo System.* & Microsoft.* coming before any others)