Remove use_allocator=none where it's implied.

scripts/slave/recipes/chromium.expected/full_chromium_fyi_ClangToTLinuxASan.json

 [
   {
     "cmd": [
       "python",
       "-u",
       "[BUILD]/scripts/slave/bot_update.py",
       "--master",
       "chromium.fyi",
       "--builder",
       "ClangToTLinuxASan",
@@ skipping 63 matching lines @@
     ]
   },
   {
     "cmd": [
       "python",
       "-u",
       "[DEPOT_TOOLS]/gclient.py",
       "runhooks"
     ],
     "env": {
-      "GYP_DEFINES": "asan=1 clang=1 clang_use_chrome_plugins=0 component=static_library lsan=1 target_arch=x64 test_isolation_mode=prepare use_allocator=none werror=''",
+      "GYP_DEFINES": "asan=1 clang=1 clang_use_chrome_plugins=0 component=static_library lsan=1 target_arch=x64 test_isolation_mode=prepare werror=''",
       "LLVM_FORCE_HEAD_REVISION": "YES"
     },
     "name": "gclient runhooks"
   },
   {
     "cmd": [
       "python",
       "-u",
       "\nimport shutil\nimport sys\nshutil.copy(sys.argv[1], sys.argv[2])\n",
       "[SLAVE_BUILD]/src/testing/buildbot/chromium.fyi.json",
@@ skipping 124 matching lines @@
       "--build_revision",
       "f27fede2220bcd326aee3e86ddfd4ebd0fe58cb9",
       "--factory-properties",
       "{\"blamelist\": [\"cool_dev1337@chromium.org\", \"hax@chromium.org\"], \"buildername\": \"ClangToTLinuxASan\", \"buildnumber\": 571, \"mastername\": \"chromium.fyi\", \"parent_buildername\": null, \"recipe\": \"chromium\", \"slavename\": \"TestSlavename\", \"workdir\": \"/path/to/workdir/TestSlavename\"}",
       "--build-properties",
       "{\"blamelist\": [\"cool_dev1337@chromium.org\", \"hax@chromium.org\"], \"buildername\": \"ClangToTLinuxASan\", \"buildnumber\": 571, \"mastername\": \"chromium.fyi\", \"parent_buildername\": null, \"recipe\": \"chromium\", \"slavename\": \"TestSlavename\", \"workdir\": \"/path/to/workdir/TestSlavename\"}"
     ],
     "name": "package build"
   }
 ]