Control Panel items are usually either *.CPL files stored in the C:\Windows\system32 directory or some command registered in the registry at
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Explorer\ControlPanel\NameSpace
or
HKEY_CURRENT_USER\SOFTWARE\Microsoft\Windows\CurrentVersion\Explorer\ControlPanel\NameSpace
Search for any CPL files in C:\Windows\System32 or open Regedit.exe and go to the above keys, then check the subitems of the above reg keys to see if the program you uninstalled has left remnants behind.
Btw, this is not related in any way to Classic Shell.