I just thought I would post this since I’ve been struggling with it for weeks, tried all the code I could find on here and nothing worked. As usual, there is a simple fix to eliminate it completely.
In Cornerstone, there are two settings in Appearance: Customize: Header:
Mobile Nav Bar Button Size
Mobile Nav Bar Button Alignment
I set these to 0, now the damn thing is gone! Yay (desired result)
I replaced it with a plug in last week and then, up till now, had two on the mobile app, but the plug-in actually works. Now I just have the plug-in.
I hope this helps some poor soul struggling with this same issue.