I'm a bit surprised, but the remaining profile managers have these rights:
Any profile manager can remove another profile manager in these cases, but it should be discussed first. Remember that managers don't own profiles. When discussing who should manage a profile or family line, think of yourselves as volunteers who are dividing up responsibility so that you can get more done.
While I have never removed a "co manager".... apparently you can. But consider why you would want to remove another descendant, etc., WikiTree is about collaboration. If there are 4 or 5 profile managers, its seems unwieldy, but who are the best profile managers... it gets complicated.
My approach, if there are fewer then 4 profile managers.... leave it at that. And if there 4 or more managers that seem responsible, I've removed myself as a PM. (Unless, perhaps it was a profile that I had spent hours and hours and hours and hours creating the biography)