[PHP 7.2] create_function() is deprecated

Humbly hoping that Drupal 7 will eventually support PHP 7.2, I will be making issues for possible incompatibilities.

create_function()is deprecated in PHP 7.2. Fortunately for us, there is only one create_function() call in whole D7 core.

I will attach a patch for your review. The only call is used as a callback function for one array_map() call. I have moved it to a standard function. This pattern was also followed in the same file.