If you are using Real-Time Shipping, it is not an option to disable the “calculate shipping” button.
If you are using both Real-Time & Custom Shipping options, there is a check-box next to the Custom Shipping option - Shop.Cart. When unchecked, this option and your Custom Shipping Methods will not be included within the calculate shipping, only the Real-Time will.
If you are using Custom Shipping only, uncheck the Shop.Cart option and the calculate shipping field will not appear on your site at all.
