staging: iio: tsl2x7x: remove power functions from tsl2X7X_platform_data

The tsl2X7X_platform_data structure contains the platform_power,
power_on, and power_off function pointers. These power management
functions should not be in the platform data. These functions were
likely used before the regulator framework was put in place. There are
no users of these functions in the mainline kernel.

Signed-off-by: Brian Masney <masneyb@onstation.org>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>