Never use the hermetic xcode toolchain for iOS recipes.

scripts/slave/recipes/ios/try.expected/gn.json

Index: scripts/slave/recipes/ios/try.expected/gn.json
diff --git a/scripts/slave/recipes/ios/try.expected/gn.json b/scripts/slave/recipes/ios/try.expected/gn.json
index 5e0338296c75767a8e2bb04ecba9b7151853832c..26938b05a83ed71542f36e035430aa1a7593f7ac 100644
--- a/scripts/slave/recipes/ios/try.expected/gn.json
+++ b/scripts/slave/recipes/ios/try.expected/gn.json
@@ -300,7 +300,6 @@
     ],
     "cwd": "[BUILDER_CACHE]/ios_simulator_gn/src",
     "env": {
-      "FORCE_MAC_TOOLCHAIN": "1",
       "GOMA_SERVICE_ACCOUNT_JSON_FILE": "/creds/service_accounts/service-account-goma-client.json"
     },
     "name": "generate_build_files (with patch)"
@@ -393,7 +392,6 @@
       "/path/to/tmp/json"
     ],
     "env": {
-      "FORCE_MAC_TOOLCHAIN": "1",
       "GOMA_SERVICE_ACCOUNT_JSON_FILE": "/creds/service_accounts/service-account-goma-client.json"
     },
     "name": "clang_revision",
@@ -446,7 +444,6 @@
     ],
     "cwd": "[BUILDER_CACHE]/ios_simulator_gn/src/out/Debug-iphonesimulator",
     "env": {
-      "FORCE_MAC_TOOLCHAIN": "1",
       "GOMA_SERVICE_ACCOUNT_JSON_FILE": "/creds/service_accounts/service-account-goma-client.json"
     },
     "name": "compile",