[13.x] Removed unneeded default argument

[AndrewMast]

Why

This is a very minor change. Recently #54876 removed unneeded function existence checks. Two of the calls were for json_validate, but only one of them passed in a depth value (512, which is the php default). This PR is removes the passing of a default value, normalizes the code to be the same in both cases of json_validate, and is based on this comment: #54876 (comment).

What

-return json_validate($value, 512);
+return json_validate($value);