Remove save_tiff() method

Since it is not specific to the IDS camera, remove the save_tiff()
method to the Camera object.  This functionality has been moved to the
save_dng() function in the tiffutils (https://github.com/ncsuarc/tiffutils)
module.

tiffutils.save_dng() only supports saving raw bayer data.  To save RGB
TIFF images, cv2.imwrite() can be used.