Hub mesh is a protocol for one hubitat hub to use devices paired to a second hubitat. Pertinently, it has nothing to do with z-wave or zigbee mesh networks.
They have to be removed. The only way to do it with a C-5 (or lower) is to use a secondary z-wave controller, like a UZB stick, and PC Controller from SiLabs.
@danabw has documented this process in detail. Here is a link to his instructions:
