Remove unused using

Author: Youssef1313

src/Microsoft.CodeAnalysis.ResxSourceGenerator/Microsoft.CodeAnalysis.ResxSourceGenerator.UnitTests/Verifiers/CSharpSourceGeneratorVerifier`1+Test.cs

@@ -22,7 +22,6 @@
 using System.Threading.Tasks;
 using Microsoft.CodeAnalysis.CSharp;
 using Microsoft.CodeAnalysis.CSharp.Testing;
-using Microsoft.CodeAnalysis.ResxSourceGenerator.CSharp;
 using Microsoft.CodeAnalysis.Testing;
 using Microsoft.CodeAnalysis.Testing.Verifiers;
 using Microsoft.CodeAnalysis.Text;