no matter whether the modules exist or not, busybox will put module info into this file:
/lib/modules/uname -r/modules.dep.bb

the file will not be made empty even the modules removed:

modprobe -v -r ip_tables

more modules.dep.bb

kernel/net/ipv4/netfilter/ip_tables.ko symbol:ipt_unregister_table symbol:ipt_register_table symbol:ipt_do_table symbol:ipt_do_table symbol:ipt_unregister_table symbol:ipt_register_table

kernel/net/ipv4/netfilter/iptable_filter.ko
ip_tables

The modules should be put into the right place, such as:
/lib/modules/uname -r/kernel/net/ipv4/netfilter

iptables tries to load ip_tables even though it is statically compiled in the kernel