Remove workflows/apidoc

Replaced with scheduled regeneration job in
https://github.com/Homebrew/rubydoc.brew.sh/pull/97.

.github/workflows/apidoc.yml

-name: Generate rubydoc.brew.sh
-on:
-  push:
-    branches: master
-jobs:
-  apidoc:
-    if: github.repository == 'Homebrew/brew'
-    runs-on: ubuntu-latest
-    steps:
-      - uses: Homebrew/actions/git-ssh@master
-        with:
-          git_user: BrewTestBot
-          git_email: homebrew-test-bot@lists.sfconservancy.org
-          key: ${{ secrets.RUBYDOC_DEPLOY_KEY }}
-
-      - name: Set up Ruby
-        uses: actions/setup-ruby@v1
-        with:
-          version: '>=2.3'
-
-      - name: Build and push API docs
-        run: |
-          # clone rubydoc.brew.sh with SSH so we can push back
-          git clone git@github.com:Homebrew/rubydoc.brew.sh
-          cd rubydoc.brew.sh
-
-          # clone latest Homebrew/brew
-          git clone --depth=1 https://github.com/Homebrew/brew
-
-          # run rake to build documentation
-          gem install bundler
-          bundle install --jobs 4 --retry 3
-          bundle exec rake
-
-          # commit and push generated files
-          git add docs
-
-          if ! git diff --exit-code HEAD -- docs; then
-            git commit -m 'docs: update from Homebrew/brew push' docs
-            git fetch
-            git rebase origin/master
-            git push
-          fi