docs: Various cleanup of outdated comments and docstrings (#31754)

- Remove pylint warning suppression from SHAKE-128 hexdigest calls; these
  are no longer needed as of astroid 2.12.12. For background, see issue
  <https://github.com/PyCQA/pylint/issues/4039>. Also, correct a comment
  that referred to SHAKE-256 instead of SHAKE-128.
- Replace "released" with "beta" in several places where there was a copy
  & paste error in dark_lang. Add mention of `beta_lang` to a docstring
  where it was omitted.
- Remove comment regarding Mongo startup; the code it referred to has since
  been removed.
- Fix typos.

.github/workflows/unit-tests.yml

@@ -44,15 +44,6 @@ jobs:
       - name: checkout repo
         uses: actions/checkout@v3
 
-      # This gives Mongo several chances to start. We started getting flakiness
-      # around 2022-02-15 wherein the start command would sometimes exit with:
-      #
-      #   * Starting database mongodb
-      #     ...fail!
-      #
-      # ...not having produced any logs or other output. We couldn't figure out
-      # what was causing Mongo to fail, so this is a (temporary?) hack to get
-      # PRs unblocked.
       - name: start mongod server for tests
         run: |
           sudo mkdir -p /data/db