We are now using the gitlab-based package workflow, the guidance on the
git-based package workflow page is out of date:

- We don't use the master branch
- We don't need the `MAINTAINED_IN_GIT.txt` file
- We no longer automatically close tasks based on tags
- We're not using Jenkins for package CI
- We don't submit packages to OBS manually

Delete the page.

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