Removes close issues step from security template

Starting with 13.3, we're early merging security merge requests
targeting master, but backports are still merged during the Security
Release process. Because of it, security issues should still be opened
until the Security Release finishes

Related to https://gitlab.com/gitlab-com/gl-infra/delivery/-/issues/1106

.gitlab/merge_request_templates/Security Release.md

@@ -23,7 +23,6 @@ See [the general developer security release guidelines](https://gitlab.com/gitla
   - [ ] Ensure it's approved by an AppSec engineer.
     - If you're unsure who should approve, find the AppSec engineer associated to the issue in the [Canonical repository], or ask #sec-appsec on Slack.
     - Trigger the [`package-and-qa` build]. The docker image generated will be used by the AppSec engineer to validate the security vulnerability has been remediated.
-  - [ ] Merge request _must_ close the corresponding security issue.
 - [ ] For a backport MR targeting a versioned stable branch (`X-Y-stable-ee`)
   - [ ] Ensure it's approved by a maintainer.