Remove duplicate tiff readers.

When opening tiff files, user was always prompted to choose between two
tiff readers. I think we need to cleanup image readers and image-series
readers, but that can happen later.

Change-Id: I25505b6f9546fe3699f7038250575044cbee0a77
Merge topic 'remove_duplicate_tiff_readers' into next

89d073e3 Remove duplicate tiff readers.