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

rust-dirstatemap: remove `set_dirstate_entry`/`set_entry` methods These methods were needed crutches before the Rust implementation caught up to Python. Calling `set_entry` (whether from Python or Rust) was dangerous since it didn't update any of the counters of the DirstateMap data structure, while having no real way of knowing when to use it "correctly" except it you were one of the 3 people who looked deep enough into the soul of this code. Differential Revision: https://phab.mercurial-scm.org/D12519