Apple has dropped the 32GB iPad mini 4 from its store and reduced the price of the 128GB model to $399. This is the second change to the device’s storage since its initial launch in 2015. Last year Apple did away with the 16GB and 64GB versions of the device and adjusted the pricing. Now the 128GB model is the only version available, but it now costs what the 16GB version did when the device first launched a year and a half ago. In addition…