cpu: do not use object_delete

CPUs are never added to the composition tree, so delete is achieved
simply by removing the last references to them.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>
diff --git a/linux-user/syscall.c b/linux-user/syscall.c
index 693e66f..a148d9f 100644
--- a/linux-user/syscall.c
+++ b/linux-user/syscall.c
@@ -5202,7 +5202,7 @@
                         NULL, NULL, 0);
           }
           thread_env = NULL;
-          object_delete(OBJECT(ENV_GET_CPU(cpu_env)));
+          object_unref(OBJECT(ENV_GET_CPU(cpu_env)));
           g_free(ts);
           pthread_exit(NULL);
       }