ILLink SDK is defined in multiple places which causes Arcade validation builds to fail #48409
Description
With dotnet/arcade@023bcee, the ILLinker is now referenced globally, similar to the compiler package. As the SDK doesn't allow to have multiple PackageReferences of the same Identitiy when IsImplicitlyDefined is set to true, the PackageReference in illink.targets should be removed.
This will unblock the Arcade validation builds: https://dev.azure.com/dnceng/internal/_build/results?buildId=998169&view=logs&j=316d5c15-0c50-544e-8051-e6b14a1ab674&t=68de0bee-b0ee-5e79-8d1a-c77a89225a17
C:\hostedtoolcache\windows\dotnet\sdk\5.0.100\Sdks\Microsoft.NET.Sdk\targets\Microsoft.NET.Sdk.DefaultItems.targets(257,5): error NETSDK1023: A PackageReference for 'Microsoft.NET.ILLink.Tasks' was included in your project. This package is implicitly referenced by the .NET SDK and you do not typically need to reference it from your project. For more information, see https://aka.ms/sdkimplicitrefs [D:\a\1\s\Build.proj]
##[error]C:\hostedtoolcache\windows\dotnet\sdk\5.0.100\Sdks\Microsoft.NET.Sdk\targets\Microsoft.NET.Sdk.DefaultItems.targets(257,5): error NETSDK1023: (NETCORE_ENGINEERING_TELEMETRY=Restore) A PackageReference for 'Microsoft.NET.ILLink.Tasks' was included in your project. This package is implicitly referenced by the .NET SDK and you do not typically need to reference it from your project. For more information, see https://aka.ms/sdkimplicitrefs
C:\hostedtoolcache\windows\dotnet\sdk\5.0.100\Sdks\Microsoft.NET.Sdk\targets\Microsoft.NET.Sdk.DefaultItems.targets(257,5): error NETSDK1023: A PackageReference for 'Microsoft.NET.ILLink.Tasks' was included in your project. This package is implicitly referenced by the .NET SDK and you do not typically need to reference it from your project. For more information, see https://aka.ms/sdkimplicitrefs [D:\a\1\s\Build.proj]
##[error]C:\hostedtoolcache\windows\dotnet\sdk\5.0.100\Sdks\Microsoft.NET.Sdk\targets\Microsoft.NET.Sdk.DefaultItems.targets(257,5): error NETSDK1023: (NETCORE_ENGINEERING_TELEMETRY=Restore) A PackageReference for 'Microsoft.NET.ILLink.Tasks' was included in your project. This package is implicitly referenced by the .NET SDK and you do not typically need to reference it from your project. For more information, see https://aka.ms/sdkimplicitrefs
C:\hostedtoolcache\windows\dotnet\sdk\5.0.100\Sdks\Microsoft.NET.Sdk\targets\Microsoft.NET.Sdk.DefaultItems.targets(257,5): error NETSDK1023: A PackageReference for 'Microsoft.NET.ILLink.Tasks' was included in your project. This package is implicitly referenced by the .NET SDK and you do not typically need to reference it from your project. For more information, see https://aka.ms/sdkimplicitrefs [D:\a\1\s\Build.proj]