The figure is inaccurate since it counts containers across all
hosts. Getting the count correct is non-trivial, so it's better to not
show the figure at all.
NB: the count still shows up on mouse-over of the link, but that is
defensible and not (very) confusing since the link represents the
image, not the image on a particular host, and it's the same count
that show up as the minor label in the container images view.
Fixes#2681.