doc: remove section about amending commits in PR guide

In my first contribution, I got the amending guidance wrongly and
amended my commit to attend some requested changes.

Amending commits is never required to author a PR in the project, and
force pushing makes reviewing harder, so the PR guide should not
recommend it as a good practice.

PR-URL: #41287
Reviewed-By: Antoine du Hamel <duhamelantoine1995@gmail.com>
Reviewed-By: Rich Trott <rtrott@gmail.com>

doc/guides/contributing/pull-requests.md

@@ -306,17 +306,10 @@ $ git push --force-with-lease origin my-branch
 ```
 
 **Important:** The `git push --force-with-lease` command is one of the few ways
-to delete history in `git`. Before you use it, make sure you understand the
-risks. If in doubt, you can always ask for guidance in the pull request.
-
-If you happen to make a mistake in any of your commits, do not worry. You can
-amend the last commit (for example if you want to change the commit log).
-
-```text
-$ git add any/changed/files
-$ git commit --amend
-$ git push --force-with-lease origin my-branch
-```
+to delete history in `git`. It also complicates the review process, as it won't
+allow reviewers to get a quick glance on what changed. Before you use it, make
+sure you understand the risks. If in doubt, you can always ask for guidance in
+the pull request.
 
 There are a number of more advanced mechanisms for managing commits using
 `git rebase` that can be used, but are beyond the scope of this guide.