Don't assume that we always have a HowToFix and remove failing test.

pkg/dart_messages/lib/generated/shared_messages.json

 {
   "exampleMessage": {
     "id": "use an Id generated by bin/message_id.dart",
     "subId": 0,
     "categories": [
       "AnalysisOptionsError"
     ],
     "template": "#use #named #arguments",
     "templateHoleOrder": [
       "arguments",
@@ skipping 625 matching lines @@
     ],
     "template": "The setter '#{memberName}' is not defined in a superclass of '#{className}'.",
     "templateHoleOrder": null,
     "howToFix": null,
     "options": null,
     "usedBy": [
       "Platform.analyzer",
       "Platform.dart2js"
     ],
     "examples": [
-      "        class A {}\n        class B extends A {\n          foo() { super.x = 499; }\n        }\n        main() { new B().foo(); }\n        ",
-      "        main() => new B().m();\n        class A {\n          get x => 1;\n        }\n        class B extends A {\n          m() { super.x = 2; }\n        }\n        "
+      "        class A {}\n        class B extends A {\n          foo() { super.x = 499; }\n        }\n        main() { new B().foo(); }\n        "
     ]
   },
   "UNDEFINED_FUNCTION": {
     "id": "ERUSKD",
     "subId": 13,
     "categories": [
       "StaticTypeWarning"
     ],
     "template": "The function '#{memberName}' is not defined.",
     "templateHoleOrder": null,
@@ skipping 39 matching lines @@
     "examples": [
       "        main() {\n          final x = 1;\n          x = 2;\n        }",
       "        main() {\n          const x = 1;\n          x = 2;\n        }\n        ",
       "        final x = 1;\n        main() { x = 3; }\n        ",
       "        const x = 1;\n        main() { x = 3; }\n        ",
       "get foo => null  main() { foo = 5; }",
       "const foo = 0  main() { foo = 5; }"
     ]
   }
 }