stemie on "[Plugin: Jetpack by WordPress.com] Jetpack Carousel not working"

You can put the code in your functions.php file of you theme.
I would not edit the code in your theme editor in WordPress back-end rather edit it in notepad++ or the like because if your functions.php file has an error in it the site will break.
Basically what you are doing is over riding the parent themes functionality in the child theme, in this case you are removing their custom gallery functionality.
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