remove duplicate moq reference

tests/ImageSharp.Tests/ImageSharp.Tests.csproj

@@ -18,7 +18,6 @@
   <ItemGroup>
     <PackageReference Include="CoreCompat.System.Drawing" Version="1.0.0-beta006" />
     <PackageReference Include="Microsoft.NET.Test.Sdk" Version="15.0.0" />
-    <PackageReference Include="Moq" Version="4.7.1" />
     <PackageReference Include="xunit" Version="2.3.0-beta4-build3742" />
     <PackageReference Include="xunit.runner.visualstudio" Version="2.3.0-beta4-build3742" />
     <PackageReference Include="Microsoft.NET.Test.Sdk" Version="15.3.0" />