Switch from yarn to pure npm

[mmattel]

This PR switches from yarn to pure npm.

• Update .drone.star
• Remove yarn.lock
• Update package.json and lint-js.js
  Switching from gulp-eslint --> gulp-eslint-new due to dependency incompatibilities
• Update README
• Added the depcheck package
  Removed all packages that were nowhere used (tested individually via remove/install/build)
  Added packages to js where missing
  npx depcheck
npx depcheck --specials eslint
  Note, not all can be removed, but we see tips where fixes are needed...

Note that yarn resolutions in package.json are overrides in npm.
The following can be added if necessary. It removes glob warnings in case of debugging asciidoc. glob will be updated on the asciidoc side whenever they are ready...

  "overrides": {
    "glob-parent": "^5.1.2"
  },

Note that now with using npm, preview using a demo Antora build is working again 😃

With this PR, all doc repos are now using npm consistently and yarn is gone.

[phil-davis]

LGTM