dirstate: use `reset_state` instead of `dropfile` in test-rebuildstate.t
As `dirstatemap.dropfile` is on its way out.
Differential Revision: https://phab.mercurial-scm.org/D11442
#require cargo test-repo
$ . "$TESTDIR/helpers-testrepo.sh"
$ cd "$TESTDIR"/../rust
Check if Cargo.lock is up-to-date. Will fail with a 101 error code if not.
$ cargo check --locked --all --quiet
However most CIs will run `cargo build` or similar before running the tests, so we need to check if it was modified
$ testrepohg diff Cargo.lock