doc: scrub mentions of asciidoc/asciidoctor

This optional dependency is now finally dropped. So ends a long journey
of trying to generate man pages in a lightweight and dependable way. The
only thing I could figure out how to make work reliably was to just
learn how to write roff myself. Yay.

.github/workflows/ci.yml

@@ -101,11 +101,6 @@ jobs:
       run: |
         ci/ubuntu-install-packages
 
-    - name: Install packages (macOS)
-      if: matrix.os == 'macos-latest'
-      run: |
-        ci/macos-install-packages
-
     - name: Install Rust
       uses: dtolnay/rust-toolchain@master
       with:

.github/workflows/release.yml

@@ -115,12 +115,6 @@ jobs:
       run: |
         ci/ubuntu-install-packages
 
-    - name: Install packages (macOS)
-      if: matrix.os == 'macos-latest'
-      shell: bash
-      run: |
-        ci/macos-install-packages
-
     - name: Install Rust
       uses: dtolnay/rust-toolchain@master
       with: