Cura 2.4 missing "split object into parts"
I don't think this feature was implemented at all with Cura v2.x. 

As the developers say on the v2.1 release, "Cura has been completely reengineered". 

Finding proper changelog documentation appears to be pretty hard because they have not posted any actual changelogs except the "user friendly viewable" changelogs which only list additions of new features but don't display what everything they changed between each version of their application.

Here is the most complete changelog I could find. I do not see any mention of this feature. https://ultimaker.com/en/products/cura-software/release-notes 

Going through the Cura 2 manual or the Cura 2.1 FAQ, also does not mention this feature.
https://ultimaker.com/en/resources/20406-installation-cura-2-1 

Furthermore, searching around for version 2 "split objects" lead to forum posts of people suggesting to use some other software to achieve this specific task. If you decide to go this route, I recommend Meshmixer from Autodesk to manipulate your models and then export to STL and import them to Cura either as a whole new position set up or separate model files where you can change them there as you need to (meshmixer allows for object repositioning around a defined build plate so you can just import the whole assembly into cura and then print).

It might also be worth to put in a feature request on the UM forums.