docs(cleanup): mark discord-control-api references as historical after in-plugin migration

CHANGELOG.md

@@ -44,7 +44,7 @@
   - supports `--install` / `--uninstall`
   - uninstall restores all recorded changes
   - writes install/uninstall records under `~/.openclaw/dirigent-install-records/`
-- Added discord-control-api with:
+- Added discord-control-api with: (historical; later migrated into plugin internal Discord REST control)
   - `channel-private-create` (create private channel for allowlist)
   - `channel-private-update` (update allowlist/overwrites for existing channel)
   - `member-list` (guild members list with pagination + optional field projection)