message: remove unneeded type checking
diff: @@ -245,16 +245,8 @@ Wallet.prototype.maximumSpendable = function maximumSpendable(params, callback)
  */
  Wallet.prototype.unspents = function(params, callback) {
  params = params || {};
  - common.validateParams(params, [], [], callback);
  -
  - const query = _.pick(params, ['limit', 'minValue', 'maxValue', 'minHeight', 'minConfirms', 'target', 'plainTarget']);
  - if (params.prevId) {
  - if (!_.isString(params.prevId)) {
  - throw new Error('invalid prevId argument, expecting string');
  - }
  - query.prevId = params.prevId;
  - }
  + const query = _.pick(params, ['prevId', 'limit', 'minValue', 'maxValue', 'minHeight', 'minConfirms', 'target', 'plainTarget']);
  return this.bitgo.get(this.url('/unspents'))
  .query(query)
  