`ByteOrder` examples have unnecessary `cfg!`

[Trevor Spiteri]

For example,

if cfg!(target_endian = "little") {
    assert_eq!(numbers, [5u32.swap_bytes(), 65000u32.swap_bytes()]);
} else {
    assert_eq!(numbers, [5, 65000]);
}

could be rewritten as

assert_eq!(numbers, [5u32.to_be(), 65000u32.to_be()]);