Remove description of "Fixes:" tag

The development process states that a "Fixes: APERTIS-<task_id>" tag
should be added to relevant commit messages. At some point we had
functionality in place to automatically add comments on the Phabricator
task when such tags were present. I don't believe that this
functionality is still in place, hence the description is missleading.

This is also not something that I have seen being used (a lot?) by core
maintainers. Since this is not common practice we should remove this
requirement, simplifying the documented process for new contributors.

Signed-off-by: Martyn Welch <martyn.welch@collabora.com>

content/guides/development_process.md

@@ -42,17 +42,6 @@ Clone the forked repository
 * Every commit must have an appropriate
   [`Signed-off-by:` tag]( {{< ref "contributions.md#sign-offs" >}} ) in
   the commit message.
-* Add a `Fixes: APERTIS-<task_id>` tag for each task in the proposed commit
-  messages (as explained in the section "Automatically closing tasks" below or
-  in the envelope message of the merge request itself) in order to link the
-  merge request to one or more tasks in Phabricator.
-* Note: The tag will ensure that Phabricator tasks are kept up-to-date with
-  regard to the status of related merge requests, through the creation of a new
-  comment with the link to the merge request every time a merge request is
-  created/updated/merged. This syntax has been chosen for the tag because it is
-  already
-  [supported by gitlab](https://docs.gitlab.com/ce/user/project/integrations/custom_issue_tracker.html).
-
 
 ## Merge Request