CLEANUP: listeners: remove the do_close argument to unbind_listener()

CLEANUP: listeners: remove the do_close argument to unbind_listener()

And also remove it from its callers. This subtle distinction was added as
sort of a hack for the seamless reload feature but is not needed anymore
since the do_close turned unused since commit previous commit ("MEDIUM:
listener: let do_unbind_listener() decide whether to close or not").
This also removes the unbind_listener_no_close() function.