Take a look at your YANG model and the delete will make sense to you. If not, see here:
Looking at the model in the examples.confd/cli/c7200/c7200.yang you have something like:
...
container router {
list bgp {
key "as-no";
leaf as-no {
type uint16;
}
container address-family {
list ipv4 {
key "unicast-multicast";
leaf unicast-multicast {
type enumeration {
enum "unicast";
enum "multicast";
}
}
}
}
}
}
and in tree format
$ pyang -f tree c7200.yang
module: c7200
...
+--rw router
+--rw bgp* [as-no]
+--rw as-no uint16
+--rw address-family
+--rw ipv4* [unicast-multicast]
+--rw unicast-multicast enumeration
...
so a delete of a list entry in the bgp list with as-no key will hence delete anything under the address family too.