Remove byteorder, use bytes::Buf::get_uint instead

[nylonicious]

byteorder was only used in one place and since bytes crate implements similar functionality it lets us drop it pretty easily.

[hkBst]

Removing byteorder is good, since it does not add much that is not already in std, but using the bytes crate here is also unnecessary. If you go explore there you'll find it does:

let slice_at = match 8.checked_sub(length_length) {
    Some(slice_at) => slice_at,
    None => panic_does_not_fit(8, length_length),
};

let mut buf = [0; 8];
buffer[..length_length].as_ref().copy_to_slice(&mut buf[slice_at..]);
return u64::from_be_bytes(buf);

If we copy the bytes into our own 8-byte buffer but start at slice_at like the code above, then the copy is just not necessary.

[nylonicious]

Thanks for pointing that out, hopefully I managed to get it right this time.