system: update checkout.

Submodule system 3e997dd..5f9933d:
> install.sh: configs: use `tar -c` | `tar -x` to exclude ".git" from
copied directories.
> configs/pool/common-assorted: add etc/dnsmasq.conf.
> configs/pool/common-assorted: etc/default-grub:
GRUB_GFXPAYLOAD_LINUX is "keep", not "auto".