Remove the need for `nightwatch.conf.js`

[Lorti]

The generated nightwatch.conf.js that simply merges the default configuration shouldn't be necessary:

https://github.com/karriereat/vue-cli-plugin-e2e-nightwatch-cucumber/blob/master/generator/template/nightwatch.conf.js

Not generating that file would be more in line with the Vue principle of "progressive disclosure" – only people who want to change the config should have to replace or extend the config file.