lftp: update 4.4.16 -> 4.5.2

Changelog: http://lftp.yar.ru/news.html#4.5.2
lftp: remove unused 'xz' expression argument

xz used to be in buildInputs but was removed in commit
d4d7931a6296cd72d3d5f360d628be86bb62246b (Cleanup: remove obsolete
references to ‘xz’, which is in stdenv).