Remove duplicate front matter keys (#621)

Fixes #620

test/built-ins/String/prototype/match/length.js

@@ -2,11 +2,12 @@
 // This code is governed by the BSD license found in the LICENSE file.
 
 /*---
-info: The length property of the match method is 1
 es5id: 15.5.4.10_A11
 es6id: 21.1.3.11
 description: Checking String.prototype.match.length
 info: >
+    The length property of the match method is 1.
+
     ES6 Section 17:
     Every built-in Function object, including constructors, has a length
     property whose value is an integer. Unless otherwise specified, this value

test/language/expressions/object/method-definition/generator-super-prop-param.js

@@ -4,11 +4,10 @@
 /*---
 info: >
  GeneratorMethod can reference SuperProperty in arg
-features: [generators]
 es6id: 14.4.1
 author: Sam Mikes
 description: GeneratorMethod uses SuperProperty (allowed)
-features: [ default-arg, generator, super ]
+features: [ default-arg, generators, super ]
 ---*/
 
 var obj = {