emulators/i386-wine-devel: Style improvements

• Reorder variables.
• Remove tools for updating pkg-plist: they were broken by precedent commits and based on the python 2 script files/mergeplist.py, but python 2 is now EOL.
• Move port-update target from Makefile.amd64 to Makefile and rename it distinfo-update as it does not update pkg-plist anymore.
• Remove EXTRACT_SUFX and use properly USES=tar:txz instead.
• Remove references to removed wine staging ports in CONFLICTS_INSTALL.

Approved by: tcberner (co-mentor)
Differential Revision: https://reviews.freebsd.org/D24550