Adjust last step on security developer template

Last step requires for all merge requests to be assigned at once, this
was added momentarily to prevent accidental merges. We now have
automatic merge request validation, so it should be necessary. This part
is also causing confusion among developers.

.gitlab/merge_request_templates/Security Release.md

@@ -30,8 +30,8 @@ See [the general developer security release guidelines](https://gitlab.com/gitla
 
 ## Maintainer checklist
 
-- [ ] Correct milestone is applied and the title is matching across all backports
-- [ ] Assigned to `@gitlab-release-tools-bot` with passing CI pipelines and **when all backports including the MR targeting master are ready.**
+- [ ] Correct milestone is applied and the title is matching across all backports.
+- [ ] Assigned to `@gitlab-release-tools-bot` with passing CI pipelines.
 
 /label ~security