Change record status: 
Project: 
Introduced in branch: 
8.x
Introduced in version: 
Description: 

The user interface for selecting a per-user theme was already removed in Drupal 7, the corresponding storage and the check was however left in place.

This has now been removed, in case a module re-added the user interface for it, it now has to handle the storage itself and provide a theme negotiator implementation.

Impacts: 
Module developers