testing: stop skipping all Python tests of Rust revlog This base class was not adapted for the introduction of `InnerRevlog`, which also stopped exposing an `Index` class from `rustext`. As a consequence, `test-rust-ancestor.py` was always skipped (and would have been slightly broken). We remove the skipping conditions from `rustancestorstest`, as they now contradict or repeat those of the base class. Also, `LazyAncestors` objects apparently hold only one reference to the inner revlog (they had previously two references on the Rust index). What matters most of course is the return to `start_count` in these tests, i.e., that there is no memory leak nor double frees. In the Python test, we conflate the presence of the `pyo3_rustext` package with that of `rustext`, as we do not plan to support building one and not the other (we hope to convert fully to PyO3 soon). The skipping is actually done by the base test class.