dirstatemap: replace `removefile` by an explicit `entry.set_untracked()` All the other caller goes through `reset_state`, so we can safely have an explicit method on `DirstateItem` object. This means that all the logic to preserve the previous state (from p2, merged, etc) is now properly encapsulated within the DirstateItem. This pave the way to using different storage for these information. Differential Revision: https://phab.mercurial-scm.org/D11315