BUG Rollback shouldn't use composer

[micmania1]

If a repository is deleted or is removed between deployments then composer install will fail and the site will be stuck in maintenance mode with no way to recover it.

[ss23]

Further, the entire rollback functionality should be reverted to "change the symlink back" instead of this incredibly complex and errorprone process it is currently IMO

[tractorcow]

I agree that this would be a better way of doing rollbacks. However, if this is actioned do so with much care not to break any of the rollback processes (smoketesting, database restore, maint pages, etc).

[chillu]

+1, this just caught me out when doing a prod release. We were relying on a temporary fork of a module in prod which had since been removed. So rollback failed with composer errors. Of course we should've kept the temp fork around in case we needed an emergency deployment, but not relying on composer would make this easier.