Prevent clicks on top-most shield for centered image nodes

Even with the fix in VisualEditor core (I2c2c592) that prevents non-sheild
elements from being interacted with on generated content nodes, in the
case of a centered image, there is a shield placed on the wrapper which
causes the same problem. By hiding that particular shield, we can get the
desired effect, of only the actual figure being clickable.

Bug: 61001
Change-Id: I7fcf1a34c5ac67c3861cf0b8f3b2447d0d7dc1c1
Merge "Prevent clicks on top-most shield for centered image nodes"