we stopped building mdbook from source (#2614)

Should of been part of 922655f as we no longer need a rust toolchain to compile mdbook

Author: tshepang

.github/workflows/bindgen.yml

@@ -237,13 +237,6 @@ jobs:
     steps:
       - uses: actions/checkout@v3
 
-      - name: Install stable
-        uses: actions-rs/toolchain@v1
-        with:
-          profile: minimal
-          toolchain: stable
-          override: true
-
       # NOTE(emilio): Change deploy-book as well if you change this.
       - name: Test book
         run: |

.github/workflows/deploy-book.yml

@@ -13,13 +13,6 @@ jobs:
         with:
           persist-credentials: false
 
-      - name: Install stable
-        uses: actions-rs/toolchain@v1
-        with:
-          profile: minimal
-          toolchain: stable
-          override: true
-
       - name: Test book
         run: |
           curl -L https://github.com/rust-lang/mdBook/releases/download/v0.4.5/mdbook-v0.4.5-x86_64-unknown-linux-gnu.tar.gz | tar xz