Support unnamed requirements directly in pip uninstall (#2577)
## Summary
In `pip uninstall`, we shouldn't need to resolve unnamed requirements,
since we already index packages in `site-packages` by their URL.
This also changes `uninstall` to ignore editables, which matches pip's
behavior.
Part of: https://github.com/astral-sh/uv/issues/313.
## Test Plan
Run `cargo run pip install ./scripts/editable-installs/black_editable`,
followed by each of the following:
- `cargo run pip uninstall ./scripts/editable-installs/black_editable`
- `cargo run pip uninstall black`
- `cargo run pip uninstall ./scripts/editable-installs/black_editable
black`
