Update deprecations issue and MR templates

.gitlab/issue_templates/Deprecations.md

@@ -53,7 +53,11 @@ Which tier is this feature available in?
 ### Links
 
 <!--
-Add links to any relevant documentation or code that will provide additional details or clarity regarding the planned change. Also, include a link to the removal issue if relevant.
+Add links to any relevant documentation or code that will provide additional details or clarity regarding the planned change.
+
+This issue is the main SSOT for the deprecations and removals process. Be sure to link all
+issues and MRs related to this deprecation/removal to this issue. This can include removal
+issues that were created ahead of time, and the MRs doing the actual deprecation/removal work.
 -->
 
 <!-- Label reminders - you should have one of each of the following labels.

.gitlab/merge_request_templates/Deprecations.md

@@ -7,9 +7,8 @@
 **Be sure to link this MR to the relevant deprecation issue(s).**
 
 - Deprecation Issue:
-- MR that deprecates the feature (optional):
 
-If there is no relevant removal or deprecation issue, hit pause and:
+If there is no relevant deprecation issue, hit pause and:
 
 - Review the [process for deprecating and removing features](https://about.gitlab.com/handbook/product/gitlab-the-product/#process-for-deprecating-and-removing-a-feature).
 - Connect with the Product Manager DRI.