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.

ci/docker/README.md

@@ -2,9 +2,8 @@ These are Docker images used for cross compilation in CI builds (or locally)
 via the [Cross](https://github.com/rust-embedded/cross) tool.
 
 The Cross tool actually provides its own Docker images, and all Docker images
-in this directory are derived from one of them. We provide our own in order
-to customize the environment. For example, we need to install some things like
-`asciidoctor` in order to generate man pages. We also install compression tools
+in this directory are derived from one of them. We provide our own in order to
+customize the environment. For example, we need to install compression tools
 like `xz` so that tests for the `-z/--search-zip` flag are run.
 
 If you make a change to a Docker image, then you can re-build it. `cd` into the

ci/macos-install-packages

@@ -1,3 +0,0 @@
-#!/bin/sh
-
-brew install asciidoctor

ci/ubuntu-install-packages

@@ -11,6 +11,4 @@ if ! command -V sudo; then
 fi
 sudo apt-get update
 sudo apt-get install -y --no-install-recommends \
-  asciidoctor \
-  zsh xz-utils liblz4-tool musl-tools \
-  brotli zstd
+  zsh xz-utils liblz4-tool musl-tools brotli zstd