builtin: spawn: don't kill the child when the child object is dropped
builtin: spawn: don't kill the child when the child object is dropped

We have `kill_all_descendants` for this.

Signed-off-by: Yuxuan Shui <7f7e1535bcd10fa942d56a3436533af20f33203f@gmail.com>

yshui/deai,yshui/deai,yshui/deai