When you have the Caldera Forms Pro API client plugin active on your site, errors and other debug information is sent to our services to help us provide better support.
This filter allows you to disable this logging:
Where Does This Code Go?
When using WordPress hooks to customize Caldera Forms or other plugins you should not modify the plugin files, or you will lose your changes when you update the plugin. Instead you should create a small plugin to hold the custom code. It's easy, learn how here.
Technically you can add the custom code to your theme's functions.php, but then you will not be able to change your theme and keep these customizations.