Quit Skype or use Windows Task Manager to kill any Skype.exe process. Go to Windows Start and in the Search/Run box type %appdata%\skype, press Enter or click the OK button. The Windows File Explorer will pop up. There locate folders named as the Skype names you want to remove from your login window. Delete these folders.
how about removing auto filled Skype names for Mac?
Please repost to Mac section.