sys: delete unused CopyFileRangeError, copy_file_error_convert, SCS_*_BINARY/GetBinaryTypeW (#31550)

Dead-code sweep of `bun_sys`.

`cargo check --workspace` passes.

## Why this code exists

| Item | Zig original | Zig callers | Status |
|---|---|---|---|
| `CopyFileRangeError` | `src/sys/copy_file.zig:5` | 0 — defined-only;
the fns return `Maybe(usize)` / `CopyFileReturnType` instead | **dead in
Zig too** |
| `copy_file_error_convert` | none — `src/bun.zig:1140` has a *dangling*
`pub const copyFileErrnoConvert = CopyFile.copyFileErrorConvert;`
re-export pointing at a fn that does not exist in `copy_file.zig` (Zig
lazy-eval hides this; 0 callers of the re-export) | n/a | **Rust-port
artifact** — created to satisfy the dangling Zig re-export; body is
identity `e.into()` |
| `SCS_*_BINARY` ×6 + `GetBinaryTypeW` re-export |
`src/sys/windows/windows.zig:116-128` | 0 — `GetBinaryTypeW` is
re-exported but never invoked (`sys.zig:3812` only mentions it in a
comment) | **dead in Zig too** — WinAPI result codes copied from
headers; the `#[allow(dead_code)]` attrs were suppressing a real signal
|