Remove redundant code

The line above already asserts that there should be no errors without using `MissingUsingsAreOk`, so the extra check does nothing

AutomaticInterface/Tests/GeneratorTests.cs

@@ -34,13 +34,6 @@ private static string GenerateCode(string code)
             .Should()
             .BeEmpty();
 
-        sourceDiagnostics
-            .Where(d => d.Severity == DiagnosticSeverity.Error)
-            .Where(x => x.Id != "CS0246")
-            .Where(x => !MissingUsingsAreOk(x))
-            .Should()
-            .BeEmpty();
-
         var generator = new AutomaticInterfaceGenerator();
 
         CSharpGeneratorDriver
@@ -56,15 +49,6 @@ out var diagnostics
         return outputCompilation.SyntaxTrees.Skip(1).LastOrDefault()?.ToString();
     }
 
-    private static bool MissingUsingsAreOk(Diagnostic x)
-    {
-        var locString = x.ToString();
-        return locString.Contains(AutomaticInterfaceGenerator.DefaultAttributeName)
-            || locString.Contains(
-                AutomaticInterfaceGenerator.IgnoreAutomaticInterfaceAttributeName
-            );
-    }
-
     [Fact]
     public void WorksWithOptionalParameters()
     {