bpo-45085: Remove the binhex module (GH-28117)

The binhex module, deprecated in Python 3.9, is now removed. The
following binascii functions, deprecated in Python 3.9, are now also
removed:

* a2b_hqx(), b2a_hqx();
* rlecode_hqx(), rledecode_hqx().

The binascii.crc_hqx() function remains available.