Remove Chromedriver as a JavaScript dependency

I just realised that I think the only time this dependency is used is if the environment variable DRUPAL_TEST_CHROMEDRIVER_AUTOSTART is set; I assume DrupalCI uses the separate chromedriver container instead.

I can't find where DRUPAL_TEST_CHROMEDRIVER_AUTOSTART is documented. Should we consider dropping this feature and dependency? It is only used in local Nightwatch tests if the environment var is set to true. It seems a bit pointless updating this dependency all the time as it should stay in sync with your local Chrome, afaik it doesn't work properly if it is too out of date. Nobody seems to be complaining about it, so I suspect nobody actually uses this feature.

Updated IS with new direction.

Not even sure we need the "local" Nightwatch test_settings any more?

#10 does not apply.

After playing with this for a bit I have a better suggestion: we can keep the DRUPAL_TEST_CHROMEDRIVER_AUTOSTART variable, but Nightwatch can handle starting Chromedriver by itself; we don't need any custom code to do this. If Chromedriver is not present, then you get a nice error message:

$ yarn test:nightwatch --env local
...
┌────────────────────────────────────────────────────────────────────────────────────────────────────┐
│                                                                                                    │
│   ChromeDriver cannot be found in the current project.                                             │
│                                                                                                    │
│    You can either install chromedriver from NPM with:                                              │
│                                                                                                    │
│       npm install chromedriver --save-dev                                                          │
│                                                                                                    │
│    or download it from https://sites.google.com/chromium.org/driver/downloads,                     │
│   extract the archive and set "webdriver.server_path" config option to point to the binary file.   │
│                                                                                                    │
│                                                                                                    │
│                                                                                                    │
└────────────────────────────────────────────────────────────────────────────────────────────────────┘

This means we can keep the environment variable but drop the dependency; anyone who was using this setup can continue as before just by installing Chromedriver themselves using the instructions.

Added CR: https://www.drupal.org/node/3319135

Discussed with @nod_, we think this should also be removed from 9.5.x.