Drop ctags indexer references and hidden api using it
The ctags indexer has been stopped a long time ago and recently got dropped from the indexer base code. As the api exposing this in the webapp is hidden, we can safely remove them.
This also fixes build [1].
Related to swh-indexer#4273 (closed)
- [1] https://jenkins.softwareheritage.org/view/swh%20master%20(draft)/job/DWAPPS/job/tests/3265/console
Migrated from D8179 (view on Phabricator)