api: Remove check on iothread_id arg in virDomainPinIOThread

Allow 0 as an iothread_id and force the hypervisor to handle.
The qemuDomainPinIOThread API will look up the iothread_id of
0 and not find it and message that anyway.

src/libvirt-domain.c

@@ -7926,7 +7926,6 @@ virDomainPinIOThread(virDomainPtr domain,
     conn = domain->conn;
 
     virCheckReadOnlyGoto(conn->flags, error);
-    virCheckPositiveArgGoto(iothread_id, error);
     virCheckNonNullArgGoto(cpumap, error);
     virCheckPositiveArgGoto(maplen, error);