Revert "Add IOperation feature flag to CSharp desktop TestOptions"

This reverts commit ca967cfe.

src/Compilers/Test/Utilities/CSharp.Desktop/TestOptions.cs

@@ -14,8 +14,7 @@ public static class TestOptions
         public static readonly CSharpParseOptions Regular = new CSharpParseOptions(kind: SourceCodeKind.Regular, documentationMode: DocumentationMode.None);
         public static readonly CSharpParseOptions RegularWithDocumentationComments = new CSharpParseOptions(kind: SourceCodeKind.Regular, documentationMode: DocumentationMode.Diagnose);
 
-        public static readonly CSharpParseOptions RegularWithIOperationFeature = Regular.WithIOperationsFeature();
-
+        
         private static readonly SmallDictionary<string, string> s_experimentalFeatures = new SmallDictionary<string, string> { { "localFunctions", "true" }, { "refLocalsAndReturns", "true" } };
         public static readonly CSharpParseOptions ExperimentalParseOptions =
             new CSharpParseOptions(kind: SourceCodeKind.Regular, documentationMode: DocumentationMode.None, languageVersion: LanguageVersion.CSharp6).WithFeatures(s_experimentalFeatures);
@@ -60,10 +59,5 @@ public static CSharpParseOptions WithStrictFeature(this CSharpParseOptions optio
         {
             return options.WithFeature("strict", "true");
         }
-
-        public static CSharpParseOptions WithIOperationsFeature(this CSharpParseOptions options)
-        {
-            return options.WithFeature("IOperation", "true");
-        }
     }
 }