lftp: bump to 4.4.15 and remove cross-compile patch.

The patch has been accepted upstream. See:
http://www.mail-archive.com/lftp-devel%40uniyar.ac.ru/msg01841.html



Signed-off-by: Arnaud Rébillout <rebillout@syscom.ch>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>