To fix conda build issues on
DM-8029, I'm changing the SpatialCellCandidate in the following ways:
- The getImage method and the _image data member have been removed from SpatialCellImageCandidate, and it is no longer templated. Its only concrete subclass, KernelCandidate, wasn't using the _image method had had to override getImage anyway.
- SpatialCellMaskedImageCandidate has been removed entirely. Its only concrete subclass, PsfCandidate, now inherits from SpatialCellImageCandidate, since that is now appropriate for MaskedImages and Images.
This is a backwards incompatible API change, albeit one to an API with very few consumers. It is also an ABI change in afw, and hence will require recompiling all downstream packages.