Method Content::getSecondaryDataUpdates was deprecates since 1.32 and moved to ContentHandler::getSecondaryDataUpdates
However, 2 deployed extensions still override this method. The extensions should start overriding ContentHandler method.
After that's done, all usages of the method should be removed. Flow is the only extension that uses it in strange way, but instead we could probably just construct a new LinksUpdate there, just copy the contents of the AbstractContent::getSecondaryDataUpdates
Usage in core DerivedPageGataUpdater can be safely removed at this point.
'SecondaryDataUpdates' hook can be removed, it's deprecated since 1.32