Sometimes you deploy iOS based devices with iTunes. There are a number of factors that can still force you into iTunes based deployments, such as needing the icons to appear a certain way in iOS. It’s not optimal but it happens. And sometimes you need to give an iPad or iPhone to a user leveraging an existing AppleID that will have a password known by multiple users. Again, not the right way, but there are design requirements that cause you to do it from time to time.
And if you’re using a shared account, one of the last things you want is for users to actually buy stuff with that shared account. Because you might have used that account and connected a credit card to it, it can come up from time to time that you then need to disable that card. Again, none of this is optimal, but it happens.
To remove the card, first open up iTunes.
From here, click on the AppleID in the upper right hand corner of the screen (the email address the account was registered with, usually) and select Account from the drop-down list.
Once the account page loads, click on Edit beside the Payment Type.
At the Edit Payment Information screen, click on None (the big red arrow isn’t actually on the screen at this point, btw).
Then click on Done and there won’t be a payment funding source attached to the account any longer. This can cause a few minor issues with deployments, but turns out way better than having tons of explicit content downloaded to devices using your organizations funds…