Revert "systemd: add module to disable network device renaming"

[pothos]

This reverts commit 6ec04c8.

Note: Needs a change in coreos-overlay to take affect.

Tested by running

./image_to_vm.sh --from=../build/images/amd64-usr/developer-… --board=amd64-usr --format=pxe
./image_to_vm.sh --from=../build/images/amd64-usr/developer-… --board=amd64-usr --format=packet
cd ../build/images/amd64-usr/developer-…
bzip2 flatcar_production_packet_image.bin

uploading them (https://eleven.dev.kinvolk.io/u/kai/), serving them from a plain HTTP server, booting via PXE (same content as https://raw.githubusercontent.com/kinvolk/flatcar-ipxe-scripts/amd64-usr/packet.ipxe except that it is served from a temporary HTTP server via mkdir server; wget ...; modify packet.ipxe; cd serve; systemd-run --system -d python3 -m http.server), downloading the Packet image to the home folder, running sudo flatcar-install -f flatcar_production_packet_image.bin.bz2 -i yourignitionwithakey -o packet -s and rebooting into the installed OS.

Related upstream issue: coreos/bugs#1767