If you have accidentally left "fpc X maintenance-menu disable" on before removing it you will need to go to the serial console and delete the entire configuration, set the root password, and commit the empty config, this deletes the VC config as well..
I'm not sure what the outcome is when a EX that has been part of a VC is joined to another one, but I suspect the outcome is not pretty.
But as Michael said, restoring to factory defaults via the front panel is the easiest way, you have to attach a new VC member with a blank (or carefull preconfigured) config.