[aur-general] delete xar and rename xar-archive to xar

[solsTiCe d'Hiver]

as xar package is unmaintained since 2007 it could be deleted and
xar-archive renamed to xar.

Of course you better notify the owners of these packages first ;-)

xar seems not to see any developped recently but may be a 1.5.3 release
will come soon.