I tried to take this issue with a tad of humor in a similar thread
That said
When you have deleted a device from Deconz you can run the service
deconz.remove_orphaned_entries
And then boot HA.
That should get rid of it
But there are still many integrations that leave garbage behind and it is still a major flaw in the generic HA UI that you cannot force a device deletion.
I find myself editing the .storage files at least once every 2nd month. There is always something that is broken that I can only remove this way.
Before anyone does this ALWAYS make backup of the files and watch out for the commas. Note that the last item in a list does not end with a comma in the json files. If you forget HA will not start. Any error in the JSON and HA will not start.