package/iputils: update path for tftpd

package/iputils: update path for tftpd

tftpd has been installed into /usr/sbin in 20210202
(in upstream commit 8d1420f tftpd: install into sbindir).

Thus remove hook which expected it in /usr/bin and tried to move it into
/usr/sbin.

Fixes:
 - http://autobuild.buildroot.net/results/3d142a705f07d496b1342e04094cd03ce7d92994
 - http://autobuild.buildroot.net/results/dae643b2d23d74b5f91225d00e85c350861a0e8a
 - http://autobuild.buildroot.net/results/dcfcb082bc188e7f990e280c3fd5d971f32cc048

Fixes: ea422f9950 ("package/iputils: bump version to 20210202")
Signed-off-by: Petr Vorel <petr.vorel@gmail.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>