Remove outdated comment

Author: ahejlsberg

src/compiler/checker.ts

@@ -5517,7 +5517,7 @@ namespace ts {
                 // (otherwise there'd be an error from hasBaseType) - this is fine, but `.members` should be reset
                 // as `getIndexedAccessType` via `instantiateType` via `getTypeFromClassOrInterfaceReference` forces a
                 // partial instantiation of the members without the base types fully resolved
-                type.members = undefined; // TODO: GH#18217
+                type.members = undefined;
             }
             return type.resolvedBaseTypes = [baseType];
         }