Remove ad-hoc images from morphology/tests/data folder.
Add a FIJI generated image to skimage/data.
The image was generated via
>>> img = binary_blobs(32, 0.05, n_dim=3, seed=1234)
>>> img = img.astype(np.uint8)*255
>>> img = img[:-2, ...]
then saved as a sequence of png frames, read into FIJI as an image sequence,
and skeletonized via Plugins -> Skeletonize (2D/3D).
