Fix other instances of checkout not using custom form class.
Fix other instances of checkout not using custom form class.

wbtuomela/cartridge,dsanders11/cartridge,wbtuomela/cartridge,traxxas/cartridge,dsanders11/cartridge,wbtuomela/cartridge,stephenmcd/cartridge,ryneeverett/cartridge,ryneeverett/cartridge,traxxas/cartridge,traxxas/cartridge,dsanders11/cartridge,stephenmcd/cartridge,ryneeverett/cartridge,stephenmcd/cartridge