media: i2c: mt9p031: Drop support for legacy platform data

No user of the mt9p031_platform_data legacy platform data for board
files exist in the kernel anymore. Drop support from the driver.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Tarang Raval <tarang.raval@siliconsignals.io>
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Hans Verkuil <hverkuil@xs4all.nl>