chore: stop publishing docs to npm

[JasonWeinzierl]

The upstream repo will publish the docs folder to npm when published. But most ESLint plugins nowadays do not do this. We can gain some space savings by removing docs from the published artifacts.

Output from npm pack before removing docs:

npm notice package size: 62.7 kB
npm notice unpacked size: 378.7 kB

After removing docs:

npm notice package size: 48.4 kB
npm notice unpacked size: 298.8 kB

[JasonWeinzierl]

Unrelated note: we could gain additional space savings by removing the CJS build and only publishing ESM.

ESM-only:

npm notice package size: 27.3 kB
npm notice unpacked size: 158.0 kB

[github-actions]

LCOV of commit 189a7da during .github/workflows/ci.yml #503

Summary coverage rate:
  lines......: 96.7% (4333 of 4479 lines)
  functions..: 96.1% (270 of 281 functions)
  branches...: no data found

Files changed coverage rate: n/a