Test runner: Detect extra property in 'actual' but not in 'expected'. (#407)

* Test runner: Detect extra property in 'actual' but not in 'expected'.

Also update all expected.json where this would result in errors.

* Include rmExpected.js script in case it is needed again

test/fixtures/jsx/basic/entity/expected.json

@@ -136,7 +136,7 @@
                 }
               },
               "extra": null,
-              "value": "\uD83D\uDCA9"
+              "value": "💩"
             }
           ]
         }
@@ -144,4 +144,4 @@
     ],
     "directives": []
   }
-}
+}