Remove CS1705 workarounds

[dougbu]

We have a fair number of CS1705 workarounds i.e. direct references to packages and projects that aren't really needed. Trick is to stop excluding @(Reference) and @(PackageReference) items in lower-level netstandard2.x projects that cause use to evaluate project dependencies incorrectly.

In particular,

• remove the extra direct references e.g. at https://github.com/dotnet/aspnetcore/blob/main/src/Components/Ignitor/src/Ignitor.csproj#L35-L36
  • we don't need to duplicate indirect references
• change Conditions to include more references e.g. at https://github.com/dotnet/aspnetcore/blob/main/src/SignalR/common/SignalR.Common/src/Microsoft.AspNetCore.SignalR.Common.csproj#L28
  • use Condition=" '$(TargetFramework)' == 'netstandard2.0' OR '$(TargetFramework)' == '$(DefaultNetFxTargetFramework)' OR '$(MSBuildRestoreSessionId)' == '' " instead
  • last bit basically means "when not restoring"

Then, backport to

• release/3.1
• release/5.0
  and
• verify shipping assemblies and .nuspec files against what release/3.1 normally produces
• verify shipping assemblies and .nuspec files against what release/5.0 normally produces

[dougbu]

/fyi @dotnet/aspnet-build

[dougbu]

/fyi @dotnet/aspnet-build I added back-ports and their verification to the issue description. Will do that once the backport bot is working.