SSRS encryption keys are broken
Ended up not trying the uninstall/reinstall of SSRS.

Here's what got me working:


Stop SSRS service
detach reporting service databases
restart SSRS -- it complains about missing DBs
stop SSRS
reattach 
restart SSRS 
Using SSRS configuration wizard, re-point SSRS to its databases
Now I was able to delete the encryption keys


This is obviously a hack solution and fails to identify what went wrong in the first place, but it worked