Removes Omnibus section from security template

Omnibus GitLab is currently moving its security development to GitLab
Security, because of it, it's no longer necessary to add the issues and
merge requests to the Security Release Tracking template.

Related to https://gitlab.com/gitlab-com/gl-infra/delivery/-/issues/692

.gitlab/issue_templates/Security Release.md

@@ -4,6 +4,10 @@
 Set the title to: `Security Release: 12.2.X, 12.1.X, and 12.0.X`
 -->
 
+:warning: **Only Release Managers and members of the AppSec team can edit the description of this issue**
+
+-------
+
 ## Releases tasks
 
 - https://gitlab.com/gitlab-org/release/docs/blob/master/general/security/release-manager.md
@@ -24,22 +28,6 @@ in the "Linked issues" section below this issue description.
 tracking issue, their merge requests may not be included in the security
 release.
 
-## Issues in Omnibus-GitLab
-
-Omnibus security fixes need to be added manually to this issue description
-using and below the following template:
-
-```markdown
-* {https://gitlab.com/gitlab-org/security/gitlab/issues/ link}
-
-| Version | MR |
-|---------|----|
-| 12.2 | {https://dev.gitlab.org/gitlab/omnibus-gitlab/merge_requests/ link} |
-| 12.1 | {https://dev.gitlab.org/gitlab/omnibus-gitlab/merge_requests/ link} |
-| 12.0 | {https://dev.gitlab.org/gitlab/omnibus-gitlab/merge_requests/ link} |
-| master | {https://dev.gitlab.org/gitlab/omnibus-gitlab/merge_requests/ link} |
-```
-
 ## QA
 {QA issue link}