[m-rev.] for review: io.primitives_{read,write}.m

[Julien Fischer]

On Sat, 12 Mar 2022, Zoltan Somogyi wrote:

> I just noticed that two of the predicates moved to io.primitives_read.m,
> putback_byte_2 and putback_uint8_2, seem to have identical implementations.
> One should be deleted with all uses replaced by the other, but which one
> should stay? I don't care, but we should pick just one.

My intention is to eventaully deprecate and then remove those
operations that represent bytes using the lower 8 bits of an int.
In that case, the version to keep is the uint8 version.

Julien.