V8: Remove infra-side gn defaults

scripts/slave/recipes/v8.expected/full_client_dart_fyi_v8_linux_release.json

 [
   {
     "cmd": [
       "python",
       "-u",
       "RECIPE_MODULE[depot_tools::bot_update]/resources/bot_update.py",
       "--master",
       "client.dart.fyi",
       "--builder",
       "v8-linux-release",
@@ skipping 117 matching lines @@
     "name": "gclient runhooks"
   },
   {
     "cmd": [
       "python",
       "-u",
       "[DEPOT_TOOLS]/gn.py",
       "--root=[SLAVE_BUILD]/v8",
       "gen",
       "[TMP_BASE]/v8_gn_tmp_1",
-      "--args=use_sysroot=false icu_use_data_file = false v8_test_isolation_mode = \"prepare\" is_debug=false target_cpu=\"x86\" use_goma=true goma_dir=\"[CACHE]/cipd/goma\""
+      "--args=is_debug=false target_cpu=\"x86\" use_goma=true goma_dir=\"[CACHE]/cipd/goma\""
     ],
     "name": "gn"
   },
   {
     "cmd": [
       "python",
       "-u",
       "[SLAVE_BUILD]/v8/tools/gyp_flag_compare.py",
       "[TMP_BASE]/v8_gn_tmp_1",
       "[SLAVE_BUILD]/v8/out/Release",
@@ skipping 110 matching lines @@
       "{\"blamelist\": [\"cool_dev1337@chromium.org\", \"hax@chromium.org\"], \"branch\": \"4.2\", \"buildername\": \"v8-linux-release\", \"buildnumber\": 571, \"mastername\": \"client.dart.fyi\", \"parent_buildername\": null, \"recipe\": \"v8\", \"revision\": \"20123\", \"slavename\": \"TestSlavename\", \"workdir\": \"/path/to/workdir/TestSlavename\"}"
     ],
     "name": "package build"
   },
   {
     "name": "$result",
     "recipe_result": null,
     "status_code": 0
   }
 ]