apertis_packaging_guide: Stop mentioning the -gitlab-update-job branches

Since we moved to an external CI config path branches like
`debian/buster-gitlab-update-job` are no  longer needed.

Signed-off-by: Emanuele Aina <emanuele.aina@collabora.com>

content/guides/apertis_packaging_guide.md

@@ -107,19 +107,21 @@ entries are kept up-to-date when the commit messages get changed via rebase.
 
 ## Pulling updates or security fixes from upstream distributions
 
-A separate set of pipeline steps are configured on the `debian/$RELEASE-gitlab-update-job`
-branches (for instance, `debian/buster-gitlab-update-job`) of each package.
+Updates coming from upstream can be pulled it by triggering a CI pipeline on a
+branches like `debian/buster` or `debian/bullseye`.
 
 The pipeline will check the Debian archive for updates, pull them in the
-`debian/$RELEASE` branch (for instance, `debian/buster`), try to merge the new
-contents with the matching `apertis/*` branches and, if successful, push a
+`debian/$RELEASE`-like branch (for instance, `debian/bullseye` or
+`debian/bullseye-security`), try to merge the new contents with the matching
+`apertis/*` branches and, if successful, push a
 proposed updates branch while creating a Merge Request for each `apertis/*`
 branches it should be landed on.
 
-The upstream update pipeline is scheduled to run automatically each weekend,
+The upstream update pipeline is usually triggered from
+[the infrastructure dashboard](https://infrastructure.pages.apertis.org/dashboard/)
 but can be manually triggered from the GitLab web UI by selecting the
 `Run Pipeline` button in the `Pipelines` page of each repository under `pkg/*`
-and selecting the `debian/buster-gitlab-update-job` branch as the reference.
+and selecting the `debian/bullseye` branch as the reference.
 
 ![Run Pipeline button](/images/run-pipeline-button.png)
 
@@ -230,7 +232,6 @@ This is the process to import a new package from Debian to Apertis:
   * changes the merge request settings:
       * only allow fast-forward merges
       * ensure merges are only allowed if pipelines succeed
-  * adds a schedule on the `debian/buster-gitlab-update-job` branch to run weekly
   * marks the `apertis/*` and `debian/*` branches as protected
 * follow the process described in the [section about landing downstream changes
   to the main archive](#landing-downstream-changes-to-the-main-archive) above to
@@ -445,9 +446,6 @@ Branches:
   but respectively target the Security and Updates repositories for published
   stable releases as described in [Process after a product
   release]( {{< ref "release-flow.md#process-after-a-product-release" >}} )
-* `debian/$DEBIAN_RELEASE-gitlab-update-job` (for instance,
-  `debian/buster-gitlab-update-job`): hosts the `debian/apertis/gitlab-ci.yaml`
-  file to configure the Debian-to-GitLab pipeline
 
 Tags:
 * `debian/*`: tags for Debian releases in the `debian/*` branches