Remove jshint

[simison]

We now have jshint and eslint to take care of code style standards. We should replace jshint with eslint.

If the current set of Jshint rules is inherited from core, there's a migration ruleset in @wordpress/eslint-plugin that we can use directly.

I see some differences between Jetpack and WordPress jshint files — could be that Jetpack one is just out of date?

There are some jshint inline rules that had been removed from JShint long time ago already:

jetpack/modules/after-the-deadline/atd-nonvis-editor-plugin.js

Line 1 in 201ec52

/* jshint devel: true, onevar: false, smarttabs: true */

PR in Gutenberg for reference WordPress/gutenberg#12840

cc @brbrr