fix: AvaloniaPublicKey.props multiple import

Warning MSB4011 "C:\GitHub\Avalonia\build\AvaloniaPublicKey.props" cannot be imported again. It was already imported at "C:\GitHub\Avalonia\Directory.Build.props (2,3)". This is most likely a build authoring error. This subsequent import will be ignored. Avalonia.Markup.Xaml.UnitTests C:\GitHub\Avalonia\tests\Avalonia.UnitTests\Avalonia.UnitTests.csproj 25

tests/Avalonia.UnitTests/Avalonia.UnitTests.csproj

@@ -22,5 +22,4 @@
   <Import Project="..\..\build\HarfBuzzSharp.props" />
   <Import Project="..\..\build\XUnit.props" />
   <Import Project="..\..\build\SharedVersion.props" />
-  <Import Project="..\..\build\AvaloniaPublicKey.props" />
 </Project>