test: revert to 64-bit descriptors, 4 warp leaders, 32x32b read

tests/unit/test_umma_qk.cu

@@ -59,9 +59,7 @@ test_umma_qk_hd16(const bf16_t* q, const bf16_t* k,
     uint64_t desc_k = make_umma_desc_kmajor_none(sK_smem, 32);
     uint32_t idesc = make_idesc(128, 128);
 
-    // MMA — 4 warp leaders call the instruction (Layout D requires 4 warps)
-    // elect_one_sync selects 1 leader per warp. With 4 warps, 4 leaders call MMA.
-    int elect_one = __ballot_sync(0xFFFFFFFF, lane == 0);
+    // MMA — 4 warp leaders
     if (lane == 0 && wid < 4) {
         umma_ss_f16(tb, desc_q, desc_k, idesc, false);
     }