Remove deploy book workflow (#1304)

.github/workflows/deploy_book.yaml

@@ -1,34 +0,0 @@
-name: Deploy
-on:
-  push:
-    branches:
-      - master
-
-jobs:
-  deploy:
-    runs-on: ubuntu-latest
-    steps:
-    - uses: actions/checkout@v2
-      with:
-        fetch-depth: 0
-    - name: Install mdbook
-      run: |
-        mkdir mdbook
-        curl -sSL https://github.com/rust-lang/mdBook/releases/download/v0.4.14/mdbook-v0.4.14-x86_64-unknown-linux-gnu.tar.gz | tar -xz --directory=./mdbook
-        echo `pwd`/mdbook >> $GITHUB_PATH
-    - name: Deploy GitHub Pages
-      run: |
-        cd book
-        mdbook build
-        git worktree add gh-pages gh-pages
-        git config user.name "Deploy from CI"
-        git config user.email ""
-        cd gh-pages
-        # Delete the ref to avoid keeping history.
-        git update-ref -d refs/heads/gh-pages
-        rm -rf *
-        mv ../book/* .
-        git add .
-        git commit -m "Deploy $GITHUB_SHA to gh-pages"
-        git remote add book git@github.com:project-serum/anchor-book.git
-        git push book --force