Strictly speaking it was the combination of the 'culture' not really being a culture, so much as a relatively small religious subset as well as having issues with the flag representing it literally meaning something else entirely (moreover, it was so small as to not have any flag or icon representing it). A poor analogy would be like using the current United States flag to represent the Confederacy; it simply wasn't accurate.
It looks like the change (
github link) was to delete everything relative to Sabbateanism, units and buildings and all in the xml (of which there were relatively few), as well as removal of a second culture with no units whatsoever linked to it. No removal of any dds or other art files though, so that should probably be updated to be commented out instead of outright deleted
@raxo2222 ?