When the actor migration stage is set to write-both and migrateActors.php hasn't been run yet, using RevDel will create entries in log_search with ls_field='target_author_actor' and empty ls_value.
This happened on Wikimedia wikis, and so needs to be cleaned up, but should not be happening anymore since migrateActors.php has already been completed.
- Patch MediaWiki so this won't happen anymore.
- Fix the maintenance script's inefficient query.
- Run maintenance to clean up existing instances of this problem on Wikimedia wikis.
This blocks setting actor migration on Wikimedia wikis to write-both/read-new.