Check SymbolFlags instead

Author: sandersn

src/compiler/checker.ts

@@ -17739,12 +17739,6 @@ namespace ts {
             }
         }
 
-        // If a symbol is a synthesized symbol with no value declaration, we assume it is a property. Example of this are the synthesized
-        // '.prototype' property as well as synthesized tuple index properties.
-        function getDeclarationKindFromSymbol(s: Symbol) {
-            return s.valueDeclaration ? s.valueDeclaration.kind : SyntaxKind.PropertyDeclaration;
-        }
-
         function getDeclarationNodeFlagsFromSymbol(s: Symbol): NodeFlags {
             return s.valueDeclaration ? getCombinedNodeFlags(s.valueDeclaration) : 0;
         }
@@ -17881,10 +17875,7 @@ namespace ts {
         }
 
         function symbolHasNonMethodDeclaration(symbol: Symbol) {
-            return forEachProperty(symbol, prop => {
-                const propKind = getDeclarationKindFromSymbol(prop);
-                return propKind !== SyntaxKind.MethodDeclaration && propKind !== SyntaxKind.MethodSignature;
-            });
+            return !!forEachProperty(symbol, prop => !(prop.flags & SymbolFlags.Method));
         }
 
         function checkNonNullExpression(