paths: delete unused Path::move_ no-op (#31551)

Dead-code sweep of `bun_paths` — single item.

`cargo check --workspace` passes.

## Why this code exists

| Item | Zig original | Zig callers | Status |
|---|---|---|---|
| `Path::move_` | `src/paths/Path.zig:288` (`move`) | 0 — the only
`.move()` hit (`src/install/hosted_git_info.zig:153`) targets
`extract.Result.move`, not `Path.move` | **dead in Zig too** — and the
Rust port is a `self`-returning no-op (Rust move semantics make it
identity) |