Drop use of openat-ext, Rust std now has efficient std::io::copy

See rust-lang/rust#75272

Author: cgwalters

Cargo.lock

@@ -52,7 +52,6 @@ ignition-config = "0.2"
 lazy_static = "^1.4"
 libc = "^0.2"
 nix = ">= 0.22, < 0.24"
-openat-ext = ">= 0.1.4, < 0.3"
 openssl = "^0.10"
 pipe = ">= 0.3, < 0.5"
 regex = ">= 1.4, < 1.6"

Cargo.toml

@@ -14,7 +14,6 @@
 
 use anyhow::{bail, Context, Result};
 use nix::unistd::isatty;
-use openat_ext::FileExt;
 use std::fs::{write, File, OpenOptions};
 use std::io::{self, copy, BufWriter, Seek, SeekFrom, Write};
 use std::os::unix::io::AsRawFd;
@@ -62,9 +61,7 @@ pub(super) fn write_live_iso(
                 .tempfile_in(output_dir)
                 .context("creating temporary file")?;
             input.seek(SeekFrom::Start(0)).context("seeking input")?;
-            input
-                .copy_to(output.as_file_mut())
-                .context("copying input to temporary file")?;
+            copy(input, output.as_file_mut()).context("copying input to temporary file")?;
             iso.write(output.as_file_mut())?;
             output
                 .persist_noclobber(&output_path)