[Docs] Remove 9.0 breaking changes from 8.x docs

docs/upgrade-notes.asciidoc

@@ -49,108 +49,6 @@ For Elastic Security release information, refer to {security-guide}/release-note
 [float]
 ==== Kibana APIs
 
-[discrete]
-[[breaking-201550]]
-.Removed legacy alerting endpoints (9.0.0)
-[%collapsible]
-====
-*Details* +
---
-* `POST /api/alerts/alert/{id?}` has been replaced by `POST /api/alerting/rule/{id?}`
-* `GET /api/alerts/alert/{id}` has been replaced by `GET /api/alerting/rule/{id}`
-* `PUT /api/alerts/alert/{id}` has been replaced by `PUT /api/alerting/rule/rule/{id}`
-* `DELETE: /api/alerts/alert/{id}` has been replaced by `DELETE /api/alerting/rule/{id}`
-* `POST /api/alerts/alert/{id}/_disable` has been replaced by `POST /api/alerting/rule/{id}/_disable`
-* `POST /api/alerts/alert/{id}/_enable` has been replaced by `POST /api/alerting/rule/{id}/_enable`
-* `GET /api/alerts/_find` has been replaced by `GET /api/alerting/rules/_find`
-* `GET /api/alerts/_health` has been replaced by `GET /api/alerting/rule/_health`
-* `GET /api/alerts/list_alert_types` has been replaced by `GET /api/alerting/rule_types`
-* `POST /api/alerts/alert/{alert_id}/alert_instance/{alert_instance_id}/_mute` has been replaced by `POST /api/alerting/rule/{rule_id}/alert/{alert_id}/_mute`
-* `POST /api/alerts/alert/{alert_id}/alert_instance/{alert_instance_id}/_unmute` has been replaced by `POST /api/alerting/rule/{rule_id}/alert/{alert_id}/_unmute`
-* `POST /api/alerts/alert/{id}/_mute_all` has been replaced by `POST /api/alerting/rule/{id}/_mute_all`
-* `POST /api/alerts/alert/{id}/_unmute_all` has been replaced by `POST /api/alerting/rule/{id}/_unmute_all`
-* `POST /api/alerts/alert/{id}/_update_api_key` has been replaced by `POST /api/alerting/rule/{id}/_update_api_key`
-* `GET /api/alerts/{id}/_instance_summary` has been deprecated without replacement. Will be removed in v9.0.0
-* `GET /api/alerts/{id}/state` has been deprecated without replacement. Will be removed in v9.0.0
---
-
-*Impact* +
-Deprecated endpoints will fail with a 404 status code starting from version 9.0.0
-
-*Action* +
-Remove references to `GET /api/alerts/{id}/_instance_summary` endpoint.
-Remove references to `GET /api/alerts/{id}/state` endpoint.
-Replace references to endpoints listed as deprecated by it's replacement. See `Details` section.
-The updated APIs can be found here https://www.elastic.co/docs/api/doc/kibana/v8/group/endpoint-alerting
-====
-
-[[breaking-201004]]
-.Removed legacy cases endpoints (9.0.0)
-[%collapsible]
-====
-*Details* +
---
-* `GET /api/cases/status` has been deprecated with no replacement. Deleted in v9.0.0
-* `GET /api/cases/{case_id}/comments` has been replaced by `GET /api/cases/{case_id}/comments/_find` released in v7.13
-* `GET /api/cases/<case_id>/user_actions` has been replaced by `GET /api/cases/<case_id>/user_actions/_find` released in v8.7
-* `includeComments` parameter in `GET /api/cases/{case_id}` has been deprecated. Use `GET /api/cases/{case_id}/comments/_find` instead, released in v7.13
---
-
-*Impact* +
-Deprecated endpoints will fail with a 404 status code starting from version 9.0.0
-
-*Action* +
-Remove references to `GET /api/cases/status` endpoint.
-Replace references to deprecated endpoints with the replacements listed in the breaking change details.
-====
-
-[[breaking-199656]]
-.Removed all security v1 endpoints (9.0.0)
-[%collapsible]
-====
-*Details* +
-All `v1` Kibana security HTTP endpoints have been removed.
-
-`GET /api/security/v1/logout` has been replaced by `GET /api/security/logout`
-`GET /api/security/v1/oidc/implicit` has been replaced by `GET /api/security/oidc/implicit`
-`GET /api/security/v1/oidc` has been replaced by GET `/api/security/oidc/callback`
-`POST /api/security/v1/oidc` has been replaced by POST `/api/security/oidc/initiate_login`
-`POST /api/security/v1/saml` has been replaced by POST `/api/security/saml/callback`
-`GET /api/security/v1/me` has been removed with no replacement.
-
-For more information, refer to {kibana-pull}199656[#199656].
-
-*Impact* + 
-Any HTTP API calls to the `v1` Kibana security endpoints will fail with a 404 status code starting from version 9.0.0.
-Third party OIDC and SAML identity providers configured with `v1` endpoints will no longer work.
-
-*Action* +
-Update any OIDC and SAML identity providers to reference the corresponding replacement endpoint listed above.
-Remove references to the `/api/security/v1/me` endpoint from any automations, applications, tooling, and scripts.
-====
-
-[discrete]
-[[breaking-193792]]
-.Access to all internal APIs is blocked (9.0.0)
-[%collapsible]
-====
-*Details* +
-Access to internal Kibana HTTP APIs is restricted from version 9.0.0. This is to ensure
-that HTTP API integrations with Kibana avoid unexpected breaking changes. 
-Refer to {kibana-pull}193792[#193792].
-
-*Impact* +
-Any HTTP API calls to internal Kibana endpoints will fail with a 400 status code starting
-from version 9.0.0.
-
-*Action* +
-**Do not integrate with internal HTTP APIs**. They may change or be removed without notice, 
-and lead to unexpected behaviors. If you would like some capability to be exposed over an
-HTTP API, https://github.com/elastic/kibana/issues/new/choose[create an issue].
-We would love to discuss your use case.
-
-====
-
 [discrete]
 [[breaking-162506]]
 .Get case metrics APIs became internal. (8.10)