If you no longer want two Pipes to be connected to each other, so if you no longer want to be able to create connected Cards, you have to disable the Connection. How to? Similar to enabling the Connection.
First, open your Pipe's settings again by clicking the Settings wheel on the top right corner of your Pipe dashboard. Scroll down to Connections:
Click the three little dots on the right side of the Connection and then select 'Delete connection'
Now, you're no longer able to create connected Cards.