Removes Calcite from the recipes of Copper Smelting and Iron Smelting. Not much to say - it's a two-line mod:

data.raw.recipe["molten-iron"].ingredients = {{type = "item", name = "iron-ore", amount = 50}}
data.raw.recipe["molten-copper"].ingredients = {{type = "item", name = "copper-ore", amount = 50}}