simplify further, changing four tests in the process

src/EditorFeatures/CSharpTest/CodeActions/IntroduceVariable/IntroduceVariableTests.cs

@@ -2479,10 +2479,10 @@ class Program
 {
     static void Main(string[] args)
     {
-        Func<int, Func<int, int>> f = x =>
+        Func<int, Func<int, int>> f = x => y =>
         {
             var {|Rename:v|} = x + 1;
-            return y => v;
+            return v;
         };
     }
 }",
@@ -2539,8 +2539,11 @@ class Program
 {
     static void Main(string[] args)
     {
-        Func<int, int> {|Rename:p|} = y => y + 1;
-        Func<int, Func<int, int>> f = x => p;
+        Func<int, Func<int, int>> f = x =>
+        {
+            Func<int, int> {|Rename:p|} = y => y + 1;
+            return p;
+        };
     }
 }");
         }
@@ -4377,11 +4380,11 @@ class TestClass
     @"using System;
 class TestClass
 {
-    Func<int, int> Y()
+    Func<int, int> Y() => f =>
     {
         const int {|Rename:V|} = 9;
-        return f => f * V;
-    }
+        return f * V;
+    };
 }";
 
             await TestInRegularAndScriptAsync(code, expected, index: 2);
@@ -4431,11 +4434,11 @@ class TestClass
     @"using System;
 class TestClass
 {
-    Func<int, int> Y()
+    Func<int, int> Y() => (f) =>
     {
         const int {|Rename:V|} = 9;
-        return (f) => f * V;
-    }
+        return f * V;
+    };
 }";
 
             await TestInRegularAndScriptAsync(code, expected, index: 2);

src/Features/CSharp/Portable/IntroduceVariable/CSharpIntroduceVariableService_IntroduceLocal.cs

@@ -28,7 +28,8 @@ internal partial class CSharpIntroduceVariableService
             bool isConstant,
             CancellationToken cancellationToken)
         {
-            var containerToGenerateInto = GetContainerToGenerateInto(document, expression, cancellationToken);
+            var containerToGenerateInto = expression.Ancestors().FirstOrDefault(s =>
+                s is BlockSyntax || s is ArrowExpressionClauseSyntax || s is LambdaExpressionSyntax);
 
             var newLocalNameToken = GenerateUniqueLocalName(
                 document, expression, isConstant, containerToGenerateInto, cancellationToken);
@@ -74,18 +75,6 @@ internal partial class CSharpIntroduceVariableService
             throw new InvalidOperationException();
         }
 
-        private SyntaxNode GetContainerToGenerateInto(
-            SemanticDocument document, ExpressionSyntax expression, CancellationToken cancellationToken)
-        {
-            var anonymousMethodParameters = GetAnonymousMethodParameters(document, expression, cancellationToken);
-            var lambdas = anonymousMethodParameters.SelectMany(p => p.ContainingSymbol.DeclaringSyntaxReferences.Select(r => r.GetSyntax(cancellationToken)).AsEnumerable())
-                .OfType<LambdaExpressionSyntax>()
-                .ToSet();
-
-            return expression.Ancestors().FirstOrDefault(s =>
-                s is BlockSyntax || s is ArrowExpressionClauseSyntax || lambdas.Contains(s));
-        }
-
         private Document IntroduceLocalDeclarationIntoLambda(
             SemanticDocument document,
             LambdaExpressionSyntax oldLambda,