Removed unused .nupkg artifact from appveyor config.
Removed unused .nupkg artifact from appveyor config.

AzureAD/microsoft-authentication-library-for-dotnet,AzureAD/microsoft-authentication-library-for-dotnet,AzureAD/azure-activedirectory-library-for-dotnet,AzureAD/microsoft-authentication-library-for-dotnet,AzureAD/microsoft-authentication-library-for-dotnet