Remove old xunit reference

Directory.Build.targets

@@ -35,7 +35,7 @@
     <!--Test Dependencies-->
     <PackageReference Update="BenchmarkDotNet" Version="0.12.0" />
     <PackageReference Update="Colourful" Version="2.0.3" />
-    <PackageReference Include="coverlet.collector" Version="1.1.0" />
+    <PackageReference Update="coverlet.collector" Version="1.1.0" />
     <PackageReference Update="Magick.NET-Q16-AnyCPU" Version="7.14.4" />
     <PackageReference Update="Microsoft.NET.Test.Sdk" Version="16.4.0" />
     <PackageReference Update="Moq" Version="4.10.0" />

tests/ImageSharp.Tests/ImageSharp.Tests.csproj

@@ -18,7 +18,6 @@
     <PackageReference Include="Magick.NET-Q16-AnyCPU" />
     <PackageReference Include="Moq" />
     <PackageReference Include="System.Drawing.Common" />
-    <PackageReference Include="xunit.runner.console" />
   </ItemGroup>
 
   <ItemGroup>