Specify that feature flags must be removed in 1 MR

- It was unclear that feature flags must be wholly removed in 1 MR. This
  change makes that more specific in the documentation.

doc/development/feature_flags/controls.md

@@ -276,17 +276,19 @@ and reduces confidence in our testing suite covering all possible combinations.
 Additionally, a feature flag overwritten in some of the environments can result
 in undefined and untested system behavior.
 
-To remove a feature flag:
+To remove a feature flag, open **one merge request** to make the changes. In the MR:
 
-1. Open a new merge request with the ~"feature flag" label so
-   release managers are aware the changes are hidden behind a feature flag.
+1. Add the ~"feature flag" label so release managers are aware the changes are hidden behind a feature flag.
 1. If the merge request has to be picked into a stable branch, add the
    appropriate `~"Pick into X.Y"` label, for example `~"Pick into 13.0"`.
    See [the feature flag process](process.md#including-a-feature-behind-feature-flag-in-the-final-release)
    for further details.
-1. Remove all references to the feature flag from the codebase.
+1. Remove all references to the feature flag from the codebase, including tests.
 1. Remove the YAML definition for the feature from the repository.
-1. Clean up the feature flag from all environments with `/chatops run feature delete some_feature`.
+
+Once the above MR has been merged, you should:
+
+1. [Clean up the feature flag from all environments](#cleanup-chatops) with `/chatops run feature delete some_feature`.
 1. Close the rollout issue for the feature flag after the feature flag is removed from the codebase.
 
 ### Cleanup ChatOps