remove unused method setKind

Author: ichiriac

src/ast.js

@@ -409,13 +409,6 @@ AST.prototype.prepare = function(kind, docs, parser) {
     result.stackUid = AST.stackUid;
   }
 
-  /**
-   * Helper to change a node kind
-   * @param {String} newKind
-   */
-  result.setKind = function(newKind) {
-    kind = newKind;
-  };
   /**
    * Sets a list of trailing comments
    * @param {*} docs