sys/mouse.h header has a definition of MOUSE_GETVARS and MOUSE_SETVARS ioctls which are not documented and only stubbed in a few drivers: mse(4), psm(4) and syscon's sysmouse(4). The only exception is MOUSE_GETVARS implemented in psm(4)
Given the fact that they were introduced 20 years ago and implementation has never been completed, remove any related code.