Don't install ESLint for github actions

These lines were added when we were trying the pronto-eslint_npm gem,
which isn't maintained anymore and is not compatible with the latest
Pronto version.

Since we're now using the pronto-eslint gem, and this gem depends on the
eslintrb gem (which includes ESLint), we don't need these lines anymore.

.github/workflows/linters.yml

@@ -13,10 +13,6 @@ jobs:
         uses: ruby/setup-ruby@v1
         with:
           bundler-cache: true
-      - name: Setup NPM
-        uses: actions/setup-node@v1
-      - name: Install eslint
-        run: npm install --global eslint@6.0.1
       - name: Run Pronto
         run: |
           PRONTO_PULL_REQUEST_ID="$(jq --raw-output .number "$GITHUB_EVENT_PATH")" PRONTO_GITHUB_ACCESS_TOKEN="${{ github.token }}" bundle exec pronto run -f github_status github_pr -c origin/${{ github.base_ref }}