I was incorrect in my previous answer. While all you really need to do is rename your Blender armature to Armature on export to remove the extra root bone in UE4, it is actually still possible to name your armature anything you want and export without the extra root bone in Blender (tested in Blender 2.93.2) if you follow this tutorial:
However, I noted I slight discrepancy between the two export methods, which I also described in the tutorial. I hope this helps!