salt.bbappend: remove iso8601 and add dateutil dependency
salt.bbappend: remove iso8601 and add dateutil dependency

SL team changed their mind and now they want dateutil instead of
iso8601. Ok. To avoid these situation in the future we'll remove these
dependencies alltogether and make the NIFeeds packages depend on them
directly.

Signed-off-by: Ioan-Adrian Ratiu <7ec73abcfe099fc5574c01312b62768070c80980@ni.com>

ni/meta-nilrt,ni/meta-nilrt,ni/meta-nilrt,ni/meta-nilrt,ni/meta-nilrt