rust-dirstatemap: remove `removefile` API
Its callers have been migrated to the newer dirstate API.
Differential Revision: https://phab.mercurial-scm.org/D12509
dirstatemap: move `set_untracked` out of the common methods
There is a dedicated Rust implementation now
Differential Revision: https://phab.mercurial-scm.org/D12507