I would bet money the customs form is still required. That's the one where you declare your imports, whether or not you are bringing in merchandise, agricultural products, meats, or over $10k cash.
I don't know if it is officially online but I found this pdf.
http://sjdloscabosairport.com/images/mexico_customs_declaration_form.pdf
You clear immigration before customs. Immigration is about you, your identification, your permission to enter. Customs is about what you are bringing with you. Mexico calls their customs Aduana.