3006 VERIFY[S,U,P] and ASSERT[S,U,P] frequently check if first argument is zero

@@ -767,11 +767,11 @@
         }
 
         for (int t = 0; t < TXG_DEFER_SIZE; t++)
                 space_map_destroy(&msp->ms_defermap[t]);
 
-        ASSERT3S(msp->ms_deferspace, ==, 0);
+        ASSERT0(msp->ms_deferspace);
 
         mutex_exit(&msp->ms_lock);
         mutex_destroy(&msp->ms_lock);
 
         kmem_free(msp, sizeof (metaslab_t));