Slim down PR template. (#18864)

.github/PULL_REQUEST_TEMPLATE.md

@@ -4,12 +4,8 @@
 ### Motivation
 <!-- What inspired you to submit this pull request? -->
 
-### Additional Notes
-<!-- Anything else we should know when reviewing? -->
-
 ### Review checklist (to be filled by reviewers)
 
 - [ ] Feature or bugfix MUST have appropriate tests (unit, integration, e2e)
-- [ ] [Changelog entries](https://datadoghq.dev/integrations-core/guidelines/pr/#changelog-entries) must be created for modifications to shipped code
 - [ ] Add the `qa/skip-qa` label if the PR doesn't need to be tested during QA.
 - [ ] If you need to backport this PR to another branch, you can add the `backport/<branch-name>` label to the PR and it will automatically open a backport PR once this one is merged