media: i2c: as3645a: Remove driver

Remove the V4L2 AS3645A sub-device driver in favour of the LED flash class
driver for the same hardware, drivers/leds/leds-as3645a.c. The latter uses
the V4L2 flash LED class framework to provide V4L2 sub-device interface.

Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Acked-by: Pavel Machek <pavel@ucw.cz>
Acked-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>