BAM!
Thank you joemikeb for having this exact issue before me. I had the same backstory (created a temp account for sake of updating my OS version prior to migrating -- then could never delete the temp account, in spite of the usual battery of tests).
Your solution worked perfectly for me.
For sake of copying your method, with a little embellishment for any noobs like myself who may have some questions:
I got everything I wanted installed/re-installed and working properly
forced a Time Machine backup
[unplugged the time machine backup and] booted from the Recovery Drive (use command-R when restarting to enter in recovery mode)
erased the boot volume (when in recovery mode, select disk utilities)
reinstalled High Sierra (an option from recovery mode)
recovered everything but the undesired account from Time Machine. (after high sierra installs the system reboots. it looks like a new mac. so one of the first options is mac migration. plug in the time machine drive and select it as the source of migration. mac migration will list the users separately, so simply de-select the undesired user and copy over everything else).
the whole process was really easy, so thank you everyone.
FWIW, my timing was a bit longer: about 2 hours to create the time machine backup (using an old drive), 1 min to erase the drive, about 1 hour to download and reinstall high sierra, and about 2 hours to restore the time machine backup. but it was mostly set-it-and-forget-it, so not a bit deal.
k
