Remove unneeded NuGet package references.

Author: jpobst

src/Xamarin.Android.Build.Tasks/Xamarin.Android.Build.Tasks.csproj

@@ -28,8 +28,6 @@
     <PackageReference Include="Mono.Cecil" Version="$(MonoCecilVersion)" GeneratePathProperty="true" />
     <PackageReference Include="ILRepack" Version="2.0.18" />
     <PackageReference Include="Irony" />
-    <PackageReference Include="NuGet.Common" Version="6.9.1" />
-    <PackageReference Include="NuGet.Packaging" Version="6.9.1" />
     <PackageReference Include="NuGet.ProjectModel" Version="6.9.1" />
     <PackageReference Include="Newtonsoft.Json" Version="$(NewtonsoftJsonPackageVersion)" />
     <PackageReference Include="System.CodeDom" />