function removeFile(id, gfs) {
    var options = {_id: id};

    if (id.constructor && id.constructor === Object) {
      options = id;
    }

    return new Promise(function (resolve, reject) {
      gfs.remove(options, function (err, result) {
        if (err) return reject(err);

        resolve(result);
      });
    });
  }
Removes a file from the db

@param id file id or options object
@param gfs GridFS