Typically, this is a case where you have to use the Windows Installer CleanUp Utility to remove the SonicEncoders MSI file. However, since this procedure is not available due to the lack of the tool's availability, Try using Revo Uninstaller. Even if it can't uninstall the application normally, it will force it to uninstall by wiping out all traces of its presence from the system.
Reboot the PC, start Revo again and locate the Sonic Encoders. It shouldn't be there anymore. At this time, the software has been discontinued properly.