Use byteorder::ReadBytesExt instead of a local implementation

[jcjones]

read_uint_le is very similar to byteorder::ReadBytesExt, as @mozkeeler pointed out:

https://github.com/jcjones/u2f-hid-rs/blob/26a203290fbb5c912fc109b97f7ba2634725f2cd/src/hidproto.rs#L137-L143

We should try switching to byteorder::ReadBytesExt (and adding it as a dependency).