Remove redundant GetDeclaredSymbol(DeclarationExpressionSyntax declarationSyntax, ...) API.

Fixes #13291.

src/Compilers/CSharp/Portable/Compilation/CSharpSemanticModel.cs

@@ -2716,9 +2716,9 @@ internal Conversion ClassifyConversionForCast(int position, ExpressionSyntax exp
         public abstract ISymbol GetDeclaredSymbol(VariableDeclaratorSyntax declarationSyntax, CancellationToken cancellationToken = default(CancellationToken));
 
         /// <summary>
-        /// Given an identifier declared in a deconstruction declaration, get the corresponding local variable symbol.
+        /// Given a variable designation syntax, get the corresponding symbol.
         /// </summary>
-        /// <param name="declarationSyntax">The syntax node that declares a variable in a deconstruction.</param>
+        /// <param name="declarationSyntax">The syntax node that declares a variable.</param>
         /// <param name="cancellationToken">The cancellation token.</param>
         /// <returns>The symbol that was declared.</returns>
         public abstract ISymbol GetDeclaredSymbol(SingleVariableDesignationSyntax declarationSyntax, CancellationToken cancellationToken = default(CancellationToken));
@@ -2731,14 +2731,6 @@ internal Conversion ClassifyConversionForCast(int position, ExpressionSyntax exp
         /// <returns>The symbol that was declared.</returns>
         public abstract ILocalSymbol GetDeclaredSymbol(DeclarationPatternSyntax declarationSyntax, CancellationToken cancellationToken = default(CancellationToken));
 
-        /// <summary>
-        /// Given an out variable declaration expression, get the corresponding symbol.
-        /// </summary>
-        /// <param name="declarationSyntax">The syntax node that declares a variable.</param>
-        /// <param name="cancellationToken">The cancellation token.</param>
-        /// <returns>The symbol that was declared.</returns>
-        public abstract ILocalSymbol GetDeclaredSymbol(DeclarationExpressionSyntax declarationSyntax, CancellationToken cancellationToken = default(CancellationToken));
-
         /// <summary>
         /// Given a labeled statement syntax, get the corresponding label symbol.
         /// </summary>
@@ -4635,8 +4627,6 @@ protected sealed override ISymbol GetDeclaredSymbolCore(SyntaxNode declaration,
                     return this.GetDeclaredSymbol((SingleVariableDesignationSyntax)node, cancellationToken);
                 case SyntaxKind.DeclarationPattern:
                     return this.GetDeclaredSymbol((DeclarationPatternSyntax)node, cancellationToken);
-                case SyntaxKind.DeclarationExpression:
-                    return this.GetDeclaredSymbol((DeclarationExpressionSyntax)node, cancellationToken);
                 case SyntaxKind.NamespaceDeclaration:
                     return this.GetDeclaredSymbol((NamespaceDeclarationSyntax)node, cancellationToken);
                 case SyntaxKind.Parameter:

src/Compilers/CSharp/Portable/Compilation/MemberSemanticModel.cs

@@ -597,12 +597,6 @@ public override ILocalSymbol GetDeclaredSymbol(DeclarationPatternSyntax declarat
             return GetDeclaredLocal(declarationSyntax, declarationSyntax.Identifier);
         }
 
-        public override ILocalSymbol GetDeclaredSymbol(DeclarationExpressionSyntax declarationSyntax, CancellationToken cancellationToken = default(CancellationToken))
-        {
-            CheckSyntaxNode(declarationSyntax);
-            return GetDeclaredLocal(declarationSyntax, declarationSyntax.Identifier());
-        }
-
         public override ILabelSymbol GetDeclaredSymbol(LabeledStatementSyntax declarationSyntax, CancellationToken cancellationToken = default(CancellationToken))
         {
             CheckSyntaxNode(declarationSyntax);

src/Compilers/CSharp/Portable/Compilation/SyntaxTreeSemanticModel.cs

@@ -1662,18 +1662,6 @@ public override ILocalSymbol GetDeclaredSymbol(DeclarationPatternSyntax declarat
             return memberModel == null ? null : memberModel.GetDeclaredSymbol(declarationSyntax, cancellationToken);
         }
 
-        /// <summary>
-        /// Given an out variable declaration expression syntax, get the corresponding symbol.
-        /// </summary>
-        /// <param name="declarationSyntax">The syntax node that declares a variable.</param>
-        /// <param name="cancellationToken">The cancellation token.</param>
-        /// <returns>The symbol that was declared.</returns>
-        public override ILocalSymbol GetDeclaredSymbol(DeclarationExpressionSyntax declarationSyntax, CancellationToken cancellationToken = default(CancellationToken))
-        {
-            var memberModel = this.GetMemberModel(declarationSyntax);
-            return memberModel == null ? null : memberModel.GetDeclaredSymbol(declarationSyntax, cancellationToken);
-        }
-
         /// <summary>
         /// Given a labeled statement syntax, get the corresponding label symbol.
         /// </summary>

src/Compilers/CSharp/Test/Semantic/Semantics/OutVarTests.cs

@@ -173,7 +173,7 @@ private static void VerifyModelForOutVar(SemanticModel model, DeclarationExpress
 
             Assert.Same(symbol, model.GetSymbolInfo(decl).Symbol);
             Assert.Equal(local.Type, model.GetTypeInfo(decl).Type);
-            Assert.Same(symbol, model.GetDeclaredSymbol(decl));
+            Assert.Null(model.GetDeclaredSymbol(decl));
 
             foreach (var reference in references)
             {