Removing index alias creation for deprecated transforms notification index

[dan-rubinstein]

Issue - https://github.com/elastic/ml-team/issues/1391

Description

In 8.x, notification indices were migrated from .data-frame-notifications-1 to .transform-notifications-000002. Extra logic was added to create an index alias from .data-frame-notifications-1 to .transform-notifications-read which is called by kibana and users to read the notification data. If a users is running on 7.x, the current guidance is to upgrade to 8.x, which will create the necessary alias and stop writing to the old notification index. We should be safe from there to stop creating the alias in the cluster listener and delete all code references in 9.x. This change deletes the alias creation logic and any remaining references to the old notification index in code.

[MERGE BLOCKER] Note: This change is blocked on the approval of the breaking change request. This change can not be merged until the breaking change request is approved.
Note [Updated]: The breaking change request has now been approved so this change does not have any more merge blockers.

Testing

• Unit tests
• Ran elasticsearch locally, created a transform and found .transform-notifications-000002 was still created with the following alias:

.transform-notifications-000002": {
        "aliases": {
            ".transform-notifications-read": {
                "is_hidden": true
            }
        }
    }

And no references to .data-frame-notifications-1 exist.

[elasticsearchmachine]

Hi @dan-rubinstein, I've created a changelog YAML for you. Note that since this PR is labelled >deprecation, you need to update the changelog YAML to fill out the extended information sections.

[elasticsearchmachine]

Pinging @elastic/ml-core (Team:ML)

[dan-rubinstein]

@elasticmachine merge upstream