Remove unused code found using periphery

Unused functions, classes, structures, and enumerations are removed by this MR. Some were left behind if they appeared to have future usefulness.

Further, there was duplicate code related to adjusting the brightness in PlayerViewController, and VideoPlayerViewController. This MR attempts to merge them appropriately. Otherwise, there should be no changes here that could even have the potential to affect runtime.

https://github.com/peripheryapp/periphery