Remove use_allocator=none where it's implied.

scripts/slave/recipes/chromium_trybot_legacy.expected/base_unittests_failure_swarming.json

 [
   {
     "cmd": [
       "python",
       "-u",
       "[BUILD]/scripts/slave/bot_update.py",
       "--master",
       "tryserver.chromium.linux",
       "--builder",
       "linux_chromium_asan_rel",
@@ skipping 180 matching lines @@
     ]
   },
   {
     "cmd": [
       "python",
       "-u",
       "[DEPOT_TOOLS]/gclient.py",
       "runhooks"
     ],
     "env": {
-      "GYP_DEFINES": "asan=1 clang=1 component=static_library dcheck_always_on=1 fastbuild=1 gomadir='[BUILD]/goma' lsan=1 target_arch=x64 test_isolation_mode=prepare use_allocator=none use_goma=1"
+      "GYP_DEFINES": "asan=1 clang=1 component=static_library dcheck_always_on=1 fastbuild=1 gomadir='[BUILD]/goma' lsan=1 target_arch=x64 test_isolation_mode=prepare use_goma=1"
     },
     "name": "gclient runhooks (with patch)"
   },
   {
     "cmd": [
       "python",
       "-u",
       "RECIPE_MODULE[isolate]/resources/find_isolated_tests.py",
       "--build-dir",
       "[SLAVE_BUILD]/src/out/Release",
@@ skipping 263 matching lines @@
     ]
   },
   {
     "cmd": [
       "python",
       "-u",
       "[DEPOT_TOOLS]/gclient.py",
       "runhooks"
     ],
     "env": {
-      "GYP_DEFINES": "asan=1 clang=1 component=static_library dcheck_always_on=1 fastbuild=1 gomadir='[BUILD]/goma' lsan=1 target_arch=x64 test_isolation_mode=prepare use_allocator=none use_goma=1"
+      "GYP_DEFINES": "asan=1 clang=1 component=static_library dcheck_always_on=1 fastbuild=1 gomadir='[BUILD]/goma' lsan=1 target_arch=x64 test_isolation_mode=prepare use_goma=1"
     },
     "name": "gclient runhooks (without patch)"
   },
   {
     "cmd": [
       "python",
       "-u",
       "RECIPE_MODULE[isolate]/resources/find_isolated_tests.py",
       "--build-dir",
       "[SLAVE_BUILD]/src/out/Release",
@@ skipping 195 matching lines @@
       "@@@STEP_LOG_LINE@python.inline@  print 'Ignored failures:'@@@",
       "@@@STEP_LOG_LINE@python.inline@  for f in failures['ignored']:@@@",
       "@@@STEP_LOG_LINE@python.inline@    print f@@@",
       "@@@STEP_LOG_LINE@python.inline@@@@",
       "@@@STEP_LOG_LINE@python.inline@sys.exit(0 if success else 1)@@@",
       "@@@STEP_LOG_END@python.inline@@@",
       "@@@STEP_FAILURE@@@"
     ]
   }
 ]