This works for SQL Server Management Studio v18.0
The file "SqlStudio.bin" doesn't seem to exist any longer. Instead my settings are all stored in this file:
C:\Users\*********\AppData\Roaming\Microsoft\SQL Server Management Studio\18.0\UserSettings.xml
- Open it in any Texteditor like Notepad++
- ctrl+f for the username to be removed
- then delete the entire
<Element>.......</Element>
block that surrounds it.