* bpo-29591: Upgrade Modules/expat to libexpat 2.2
* bpo-29591: Restore Python changes on expat
* bpo-29591: Remove expat config of unsupported platforms
Remove the configuration (Modules/expat/*config.h) of unsupported
platforms:
* Amiga
* MacOS Classic on PPC32
* Open Watcom
* bpo-29591: Remove useless XML_HAS_SET_HASH_SALT
The XML_HAS_SET_HASH_SALT define of Modules/expat/expat.h became
useless since our local expat copy was upgrade to expat 2.1 (it's now
expat 2.2.0).
with it a vareity of bug fixes, both security and behavior. See
http://www.libexpat.org/ for the list.
NOTE: I already backported the expat hash randomization fix in March.
Fixes issue #14340.