[Merge] lp:~dannf/debian-installer/arm64-cleanup into lp:~ubuntu-core-dev/debian-installer/ubuntu

[dann frazier]

fyi, this should take care of the necessary lp:maas-images changes:
 https://code.launchpad.net/~dannf/maas-images/arm64-netinst-restructure/+merge/250338
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https://code.launchpad.net/~dannf/debian-installer/arm64-cleanup/+merge/249738
Your team Ubuntu Core Development Team is requested to review the proposed merge of lp:~dannf/debian-installer/arm64-cleanup into lp:~ubuntu-core-dev/debian-installer/ubuntu.