Remove the scoped publish-wiki workflow and the marker path (2.0.0)

- .gitea/scoped_workflows/publish-wiki.yml is deleted
- tools/publish_wiki.py requires WIKI_PRUNE, reads no marker, and defaults
  WIKI_DIR to docs/wiki; its tests follow
- README, onboarding, troubleshooting and upgrading guides, and the wiki pages
  in English, Danish and Bahasa Malaysia no longer describe the scoped workflow
- changelog entry 2.0.0 with the Breaking group

Task: MIL-009#6
Task: MIL-009#8

tests/workflow_source.py

@@ -13,7 +13,6 @@ WORKFLOW_DIRS = (
 )
 SYNC_WORKFLOW = WORKFLOW_DIRS[0] / "sync-github-metadata.yml"
 SYNC_SCRIPT = REPO_ROOT / "tools" / "sync_github_metadata.py"
-PUBLISH_WORKFLOW = WORKFLOW_DIRS[0] / "publish-wiki.yml"
 PUBLISH_SCRIPT = REPO_ROOT / "tools" / "publish_wiki.py"
 
 _HEREDOC = re.compile(