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.