Old watcher templates are not actually deleted

[masseyke]

Before we used system indices in watcher in 8.0, the component templates .triggered_watches and .watches were used to create the watcher indices. We have this ticket to delete them. But I think that that change only deletes old-style templates, not component templates. So the component templates remain, and we get this error on upgrade to ES 9:

unable to create new index [.triggered_watches-reindexed-for-9] from feature [watcher] because it would match composable template [.triggered_watches]

The workaround is to delete the component templates:

DELETE _index_template/.triggered_watches
DELETE _index_template/.watches

and to start watcher manually:

POST /_watcher/_start

[elasticsearchmachine]

Pinging @elastic/es-data-management (Team:Data Management)