Drop the tftpd binary, which is no longer provided upstream.  Users
should switch to the atftp server as a replacement.

Avoid executing runtime tests, which are not supported in cross-build
environments.

Signed-off-by: Noah Meyerhans <frodo@morgul.net>

Signed-off-by: Rosen Penev <rosenp@gmail.com>

Move the tftpd binary from /usr/bin to /usr/sbin per upstream.

Signed-off-by: Noah Meyerhans <frodo@morgul.net>

Signed-off-by: Noah Meyerhans <frodo@morgul.net>

Per discussion in https://github.com/openwrt/openwrt/pull/1804, iputils is
moving from the main openwrt repository to the packages feed, and is switching
from the abandoned skbuff.net upstream to github.com/iputils/iputils

Signed-off-by: Noah Meyerhans <frodo@morgul.net>