I have a transform node that is linked to a motionfx chop.

Overridden by /obj/geo1/motionfx/tx_export1 transform1:tx

when I right-click, I don't have the option to delete channel. When I delete the whole transform node and create a new one, it's back again.

Got it! You have to go into the CHOP and find the node that is exported and delete the path to the node in its properties.

You can also just disable the export coming out of CHOPs.

From http://www.sidefx.com/docs/houdini/network/motioneffects [sidefx.com]

- Right-click a parameter and open the Motion Effects submenu.
- Turn off the Enable effect checkbox item.