fix(Guild): equals method modifying features array of guild (#2544)

* Fixed a bug where Guild#equals would cause the given guild to lose its features

* Fix Util.arraysEqual

* Fixed docs for Util.arraysEqual

* Remove Util.arraysEqual

src/util/Util.js

@@ -118,25 +118,6 @@ class Util {
     return { animated: Boolean(m[1]), name: m[2], id: m[3] };
   }
 
-  /**
-   * Checks whether the arrays are equal, also removes duplicated entries from b.
-   * @param {Array<*>} a Array which will not be modified.
-   * @param {Array<*>} b Array to remove duplicated entries from.
-   * @returns {boolean} Whether the arrays are equal.
-   * @private
-   */
-  static arraysEqual(a, b) {
-    if (a === b) return true;
-    if (a.length !== b.length) return false;
-
-    for (const item of a) {
-      const ind = b.indexOf(item);
-      if (ind !== -1) b.splice(ind, 1);
-    }
-
-    return b.length === 0;
-  }
-
   /**
    * Shallow-copies an object with its class/prototype intact.
    * @param {Object} obj Object to clone