[Security] Remove 9.0.4 release notes (#2132)

Removes 9.0.4 Security release notes since the release has been
postponed.

Author: natasha-moore-elastic

release-notes/elastic-security/index.md

@@ -27,22 +27,6 @@ To check for security updates, go to [Security announcements for the Elastic sta
 
 % *
 
-## 9.0.4 [elastic-security-9.0.4-release-notes]
-
-### Features and enhancements [elastic-security-9.0.4-features-enhancements]
-* Improves logging of fatal exceptions in {{elastic-defend}}.
-
-### Fixes [elastic-security-9.0.4-fixes]
-* Fixes differences between risk scoring preview and persisted risk scores [#226456]({{kib-pull}}226456).
-* Updates a placeholder and validation message in the **Related Integrations** section of the rule upgrade flyout [#225775]({{kib-pull}}225775).
-* Excludes {{ml}} rules from installation and upgrade checks for users with Basic or Essentials licenses [#224676]({{kib-pull}}224676).
-* Allows using days as a time unit in rule schedules, fixing an issue where durations normalized to days were incorrectly displayed as 0 seconds [#224083]({{kib-pull}}224083).
-* Strips `originId` from connectors before rule import to ensure correct ID regeneration and prevent errors when migrating connector references on rules [#223454]({{kib-pull}}223454).
-* Fixes an issue that prevented the AI Assistant Knowledge Base settings UI from displaying [#225033]({{kib-pull}}225033).
-* Fixes a bug in {{elastic-defend}} where Linux network events would fail to load if IPv6 is not supported by the system.
-* Fixes an issue in {{elastic-defend}} that may result in bugchecks (BSODs) on Windows systems with a very high volume of network connections. This issue has only been observed on Windows Server.
-* Fixes an issue where {{elastic-defend}} may incorrectly set the artifact channel in policy responses, and adds `manifest_type` to policy responses.
-
 ## 9.0.3 [elastic-security-9.0.3-release-notes]
 
 ### Features and enhancements [elastic-security-9.0.3-features-enhancements]