Removeextupd

Before this is merged we need to decide on a policy for the mediawiki-core repo.

My plan would be to no longer use tracking branches, instead defining each commit to checkout within the repo itself.
This would also stop us from having any unexpected deployments of updates by extensions updating their branches and we would know exactly what code is deployed at any time.

Doing this and removing the task for updating submodules (which is instead done within the MW git pull) speeds up the whole ansible-pull dramatically