Revert #96 when and if that becomes possible

# 💡 Summary #

#96 should be reverted when and if that becomes possible.

## Motivation and context ##

canonical/cloud-init#4764 suggests that `cloud-init` allow for the user to specify Netplan DHCP options. If implemented, this change would mean that we would no longer need to fix the Netplan configuration generated by `cloud-init`.

See also cisagov/skeleton-packer#300.

Start by reviewing issue #96 and canonical/cloud-init#4764 to determine whether cloud-init now supports user-specified Netplan DHCP options. Check the Terraform module changes introduced by #96; the work is done when that upstream capability exists and the #96 changes can be safely reverted.

Written by the indexing model from the issue text.