undo hack in Benchmarks

Author: antonfirsov

tests/ImageSharp.Drawing.Benchmarks/ImageSharp.Drawing.Benchmarks.csproj

@@ -3,8 +3,7 @@
   <PropertyGroup>
     <OutputType>Exe</OutputType>
     <RootNamespace>SixLabors.ImageSharp.Drawing.Benchmarks</RootNamespace>
-<!--    <TargetFrameworks>netcoreapp3.1;netcoreapp2.1;net472</TargetFrameworks>-->
-    <TargetFrameworks>netcoreapp3.1</TargetFrameworks>
+    <TargetFrameworks>netcoreapp3.1;netcoreapp2.1;net472</TargetFrameworks>
     <IsPackable>false</IsPackable>
     <GenerateProgramFile>false</GenerateProgramFile>
     <!--Used to hide test project from dotnet test-->