This removes use of Cython's typed memoryviews.
This reverts commit b5d9106966: "ENH: Use Cython data types instead of Numpy dtypes."
Conflicts:
skimage/morphology/_greyreconstruct.pyx
In particular, it wasn't clear whether `image` was the seed image or the mask image rnd `values` was used to refer to both image intensity values and their rank-order.