Remove IgnoredDuplicateType once cleaned up in WPF

[dagood]

dotnet/core-setup#6817 (comment)

https://github.com/dotnet/core-setup/blob/f40e2ca284dab1abf2a33b6ae7c19c52e372500c/src/pkg/projects/windowsdesktop/pkg/Microsoft.WindowsDesktop.App.pkgproj#L30-L43

[ojhad]

Types have been removed from WPF as part of this PR: dotnet/wpf#1000

[dagood]

Complete: master dotnet/core-setup#7868, 3.0 dotnet/core-setup#7970.