To uninstall Ecamm Live's System Audio plugin, choose Uninstall System Audio... from the Ecamm Live menu at the top of the screen beside the  menu.

To uninstall Ecamm Live's Virtual Camera plugin, choose Uninstall Virtual Cam...  from the Outputs ➝ Virtual Cam menu at the top of the screen.

To uninstall the Ecamm Live app, drag the Ecamm Live icon in your Applications folder to your Mac's trash.