Remove `uv pip sync` suggestion with `pyproject.toml` (#14510)
## Summary
I think doing this would almost always be a mistake, since it won't
install any transitive dependencies. Instead, I took the opportunity to
mention the `pylock.toml` format.
Closes
https://github.com/astral-sh/uv/issues/14507#issuecomment-3050083116.
