rust-dirstatemap: use `DirstateEntry::tracked` directly
`state()` is a legacy API that will be removed at some point, let's use the
newer API.
Differential Revision: https://phab.mercurial-scm.org/D12521
rust-cpython: remove unused API to `drop_entry_and_copy_source`
This is not used anywhere anymore and its use cases are covered by the new API
Differential Revision: https://phab.mercurial-scm.org/D12520