[Security Solution] Delete route handlers for deprecated bulk endpoints

[nikitaindik]

Previous work for context: #193184

Summary

We have unregistered the deprecated bulk endpoints from router in main/v9. Now we need to fully remove the code.

AC:

• Deprecated bulk endpoint handlers should be removed from main and v9 branches (but they should stay in v8)
• Related tests, unused utils and any other dead code should be removed

List of deprecated bulk endpoints

Method	Endpoint
POST	/api/detection_engine/rules/_bulk_create
PUT	/api/detection_engine/rules/_bulk_update
PATCH	/api/detection_engine/rules/_bulk_update
DELETE	/api/detection_engine/rules/_bulk_delete
POST	/api/detection_engine/rules/_bulk_delete

Todo

• Delete the route handlers and all the associated code
• Address TODO: https://github.com/elastic/kibana/issues/193184 comments

[elasticmachine]

Pinging @elastic/security-solution (Team: SecuritySolution)

[elasticmachine]

Pinging @elastic/security-detections-response (Team:Detections and Resp)

[elasticmachine]

Pinging @elastic/security-detection-rule-management (Team:Detection Rule Management)

[banderror]

@jkelas This is another issue related to the removed bulk CRUD endpoints.

Besides removing the docs for the bulk CRUD API, we will need to clean up the code and remove the bulk CRUD handlers, as well as any leftover code related to them, so that we don't leave any unused code in the repo. I guess this was already on you list to do.

I added this ticket to the epic.