Updates security MR template

Highlights security merge request must mention the security issue they
belong to. Also removes some items from the issue template, as they're
no longer necessary

.gitlab/issue_templates/Security developer workflow.md

@@ -50,10 +50,6 @@ After your merge request has being approved according to our [approval guideline
 | -------- | -------- |
 | Issue on [GitLab](https://gitlab.com/gitlab-org/gitlab/issues) | #TODO  |
 | Security Release tracking issue | #TODO  |
-| `master` MR | !TODO   |
-| `Backport X.Y` MR | !TODO   |
-| `Backport X.Y` MR | !TODO   |
-| `Backport X.Y` MR | !TODO   |
 
 ### Details
 

.gitlab/merge_request_templates/Security Release.md

@@ -8,11 +8,11 @@ See [the general developer security release guidelines](https://gitlab.com/gitla
 
 ## Related issues
 
-<!-- Mention the issue(s) this MR is related to -->
+<!-- Mention the GitLab Security issue this MR is related to -->
 
 ## Developer checklist
 
-- [ ] Link this MR in the `links` section of the related issue on [GitLab Security].
+- [ ] **Make sure this merge request mentions the [GitLab Security] issue it belongs to (i.e. `Related to <issue_id>`).**
 - [ ] Merge request targets `master`, or `X-Y-stable` for backports.
 - [ ] Milestone is set for the version this merge request applies to. A closed milestone can be assigned via [quick actions].
 - [ ] Title of this merge request is the same as for all backports.