leds: pca9685: Remove leds-pca9685 driver

This driver is replaced by pwm-pca9685 driver and there is no user uses this
driver in current tree. So remove it.

Signed-off-by: Axel Lin <axel.lin@ingics.com>
Acked-by: Steffen Trumtrar <s.trumtrar@pengutronix.de>
Acked-by: Maximilian Güntner <maximilian.guentner@gmail.com>
Signed-off-by: Bryan Wu <cooloney@gmail.com>