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/esprima/es2015-export-declaration/export-default-function/expected.json

@@ -59,6 +59,7 @@
           "id": null,
           "generator": false,
           "expression": false,
+          "async": false,
           "params": [],
           "body": {
             "type": "BlockStatement",