[test]: drop redundant attn_qat_infer capability test (superseded by #1647)

The hardening commit added fastvideo/tests/attention/test_attn_qat_infer_
capability.py to assert is_attn_qat_infer_available() gates on device
capability. #1647 (same author) since landed test_attn_qat_infer_arch_gate.py
on main — a strict superset that parametrizes the full sm_12x-CUTLASS /
sm_100-103-FA4 resolution (incl. the same is_attn_qat_infer_available assertion)
plus receipts, forward-dispatch safety, memoization and opcheck. The older test
also asserted the now-stale (10,0)->False (pre-#1647 FA4 support), reddening CI.
Remove it and its pr_test lane entry; arch_gate.py is the single source of truth.

Author: Mister-Raggs

fastvideo/tests/attention/test_attn_qat_infer_capability.py

@@ -383,7 +383,6 @@ def run_unit_test():
         "./fastvideo/tests/stages/ ./fastvideo/tests/ops/ ./fastvideo/tests/worker/ "
         "./fastvideo/tests/training/test_trackers.py "
         "./fastvideo/tests/attention/test_sdpa_metadata_mask_contract.py "
-        "./fastvideo/tests/attention/test_attn_qat_infer_capability.py "
         "./fastvideo/tests/modal/test_kernel_build_cache.py ./fastvideo/tests/modal/test_pr_test.py "
         "./fastvideo/tests/modal/test_ssim_test.py "
         "--ignore=./fastvideo/tests/entrypoints/test_openai_api_integration.py "