Kept the infrastructure to allow re-introducing it later if a better source for a device key is found.
Added support for not having any valid settings encryption key.
Added warnings if the user is running without a settings encryption key.
Added additional checks during startup to help with troubleshooting and configuring a setup with a settings encryption key.
Docker builds will now warn if no encryption key is set.
This fixes#5518
The last references were removed in 5170c6ad1d ("Remove unused
CommonStrings class"), but the last real usages were removed in revision
62c75d9af9 ("Removed all informs code (no more 1.3.x UI)").
