[tests] fix NU1510 warning as error (#1306)

Context: NuGet/NuGet.Client#6239

.NET 10 Preview 1 enables `$(RestoreEnablePackagePruning)=true` by
default.

This produces multiple warnings as errors in dotnet/android:

    external\Java.Interop\tests\Java.Interop.Dynamic-Tests\Java.Interop.Dynamic-Tests.csproj :
    error NU1510: Warning As Error: PackageReference Microsoft.CSharp will not be pruned. Consider removing this package from your dependencies, as it is likely unnecessary.

The `Microsoft.CSharp` package does seem like it can just be removed.

Author: jonathanpeppers

tests/Java.Interop.Dynamic-Tests/Java.Interop.Dynamic-Tests.csproj

@@ -13,7 +13,6 @@
   </PropertyGroup>
 
   <ItemGroup>
-    <PackageReference Include="Microsoft.CSharp" />
     <PackageReference Include="Microsoft.NET.Test.Sdk" />
     <PackageReference Include="nunit" />
     <PackageReference Include="NUnit.ConsoleRunner" />