Removes Security Release Tracking issue template

This issue is now generated automatically at the end of each security
release, so we no longer need to keep the template under
'/issue_templates/'

Related to https://gitlab.com/gitlab-com/gl-infra/delivery/-/issues/1144

.gitlab/issue_templates/Security Release Tracking Issue.md

-<!--
-# Read me first!
-
-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**
-
--------
-
-## Version issues:
-
-12.2.X, 12.1.X, 12.0.X: {release task link}
-
-## Issues in GitLab Security
-
-To include your issue and merge requests in this Security Release, please mark
-your security issues as related to this release tracking issue. You can do this
-in the "Linked issues" section below this issue description.
-
-:warning: If your security issues are not marked as related to this release
-tracking issue, their merge requests will not be included in the security
-release.
-
-### Branches to target in GitLab Security
-
-Your Security Implementation Issue should have `4` merge requests associated:
-
-- [master and 3 backports](https://gitlab.com/gitlab-org/release/docs/-/blob/master/general/security/developer.md#backports)
-- Backports should target the stable branches for the versions mentioned included in this Security Release
-
-## Blog post
-
-Security: {https://gitlab.com/gitlab-org/security/www-gitlab-com/merge_requests/ link}<br/>
-GitLab.com: {https://gitlab.com/gitlab-com/www-gitlab-com/merge_requests/ link}
-
-## Email notification
-{https://gitlab.com/gitlab-com/marketing/general/issues/ link}
-
-/label ~security ~"upcoming security release"
-/confidential