[mle] unify the way of child removing
[mle] unify the way of child removing

Signed-off-by: Duda, Lukasz <714d933c7fb37343dcea36d8abaf85e065f4c5bc@nordicsemi.no>

srickardti/openthread,bukepo/openthread,lanyuwen/openthread,librasungirl/openthread,erja-gp/openthread,pvanhorn/openthread,xiaom-GitHub/openthread,LeZhang2016/openthread,abtink/openthread,gandreello/openthread,srickardti/openthread,chshu/openthread,mszczodrak/openthread,turon/openthread,turon/openthread,srickardti/openthread,mszczodrak/openthread,bukepo/openthread,bukepo/openthread,LeZhang2016/openthread,chshu/openthread,xiaom-GitHub/openthread,georgecpr/openthread,openthread/openthread,gandreello/openthread,georgecpr/openthread,erja-gp/openthread,mszczodrak/openthread,jwhui/openthread,lanyuwen/openthread,chshu/openthread,abtink/openthread,erja-gp/openthread,gandreello/openthread,librasungirl/openthread,erja-gp/openthread,openthread/openthread,chshu/openthread,chshu/openthread,LeZhang2016/openthread,georgecpr/openthread,abtink/openthread,lanyuwen/openthread,srickardti/openthread,pvanhorn/openthread,openthread/openthread,erja-gp/openthread,xiaom-GitHub/openthread,pvanhorn/openthread,bukepo/openthread,erja-gp/openthread,mszczodrak/openthread,LeZhang2016/openthread,gandreello/openthread,xiaom-GitHub/openthread,LeZhang2016/openthread,pvanhorn/openthread,lanyuwen/openthread,jwhui/openthread,georgecpr/openthread,mszczodrak/openthread,lanyuwen/openthread,abtink/openthread,georgecpr/openthread,pvanhorn/openthread,librasungirl/openthread,georgecpr/openthread,gandreello/openthread,chshu/openthread,openthread/openthread,jwhui/openthread,xiaom-GitHub/openthread,xiaom-GitHub/openthread,turon/openthread,librasungirl/openthread,mszczodrak/openthread,pvanhorn/openthread,LeZhang2016/openthread,jwhui/openthread,lanyuwen/openthread,gandreello/openthread,turon/openthread