Remove [[:Category:Italian verb forms]] when {{temp|head|it|verb form}} is present.

Load the entire category and skip if does not contain the string {{head|it|verb form. That's why the list is so big.

Yes that's what a simple Python bot would do too. But that way you don't know whether you skipped any, nor which still need to be done. My proposal would work around that, but at the cost of temporarily emptying out the category.