V8: Remove deprecated test-runner flag

scripts/slave/recipes/v8.expected/full_client_v8_V8_Win64___debug.json

 [
   {
     "cmd": [
       "python",
       "-u",
       "RECIPE_PACKAGE_REPO[build]\\scripts\\slave\\kill_processes.py"
     ],
     "name": "taskkill"
   },
   {
@@ skipping 878 matching lines @@
       "--mode",
       "Debug_x64",
       "--arch",
       "x64",
       "--outdir",
       "out",
       "--buildbot",
       "--timeout=200",
       "--random-seed=-564235616",
       "bot_default",
-      "--ignition-turbofan",
       "--variants=ignition_turbofan",
       "--rerun-failures-count=2",
       "--swarming",
       "--json-test-results",
       "${ISOLATED_OUTDIR}/output.json"
     ],
     "name": "[trigger] Ignition - turbofan on Windows-7-SP1",
     "~followup_annotations": [
       "@@@STEP_LOG_LINE@json.output@{@@@",
       "@@@STEP_LOG_LINE@json.output@  \"base_task_name\": \"Ignition - turbofan/Windows-7-SP1/[dummy has/V8 Win64 - debug/571\", @@@",
@@ skipping 242 matching lines @@
       "@@@STEP_LOG_LINE@durations@Duration: 00:00:101@@@",
       "@@@STEP_LOG_END@durations@@@"
     ]
   },
   {
     "name": "$result",
     "recipe_result": null,
     "status_code": 0
   }
 ]