image: remove not required dependency

Remove no longer required dependeny to healthy.

Signed-off-by: Mario Schuknecht <m.schuknecht@dresearch.de>
ntp: remove workaround

Remove workaround for an outdated ntpdate.bbappend (4.2.6p3).

Signed-off-by: Mario Schuknecht <m.schuknecht@dresearch.de>