Change record status: 
Project: 
Introduced in branch: 
8.9.x
Introduced in version: 
8.9.0
Description: 

system_user_timezone() is a helper method for System module's form alters of the user account forms. These form alters have been removed so this method is no longer required by core. If your custom module is using this method it should copy the code.

Impacts: 
Module developers