When a Tarantool C API function is used for the first time from a user thread (box_region_alloc, for example), the thread is renamed to "unknown". It doesn't seem right - the user could already set the thread name according to the thread's purpose. We shouldn't set names of user threads at all.

It's happening because of CordOnDemand. Let's simply remove thread renaming from there.

Jira issue: https://jira.vk.team/browse/TNTP-5710