clean up lib/parse.js (#2047)

- remove unused definitions
- replace `array_to_hash()`

lib/utils.js

@@ -43,13 +43,6 @@
 
 "use strict";
 
-function array_to_hash(a) {
-    var ret = Object.create(null);
-    for (var i = 0; i < a.length; ++i)
-        ret[a[i]] = true;
-    return ret;
-};
-
 function slice(a, start) {
     return Array.prototype.slice.call(a, start || 0);
 };