MoveOrCopyImageGroup - perform unlock when neccessary to avoid deadlock

When attempting to revert by executing RemoveImage, there's no need to
unlock the image.

Reasons:
1. It's going to be removed by RemoveImage.
2. The transaction isn't ended when calling RemoveImage, which attempts
to update the same db record, causing to a deadlock.

Change-Id: I3ea9bccb7e1a055613bb9a86d77e784e29f94bc5
Signed-off-by: Liron Aravot <laravot@redhat.com>