Don't recommend changing javascript_driver config

`javascript_driver` is a configuration value that changes the driver used for *all* scenarios tagged with `@javascript` after it is set. That means that it impacts tests that are run after a `@billy` test. For me, this manifested as a test suite that froze partway through and timed out. Our `@billy` tests should not impact other tests, and setting `current_driver` is sufficient to make sure this test uses billy, regardless of the presence of `@javascript`.