[ios] Don't use GOMA on xcode_clang FYI builder.

NOTRY=true

Bug: 843236
Cq-Include-Trybots: luci.chromium.try:ios-simulator-full-configs;master.tryserver.chromium.mac:ios-simulator-cronet
Change-Id: Ibfc9e785a0846c458eeb230e6545603fef5c13d2
Reviewed-on: https://chromium-review.googlesource.com/1089139Reviewed-by: John Budorick <jbudorick@chromium.org>
Commit-Queue: Justin Cohen <justincohen@chromium.org>
Cr-Commit-Position: refs/heads/master@{#564951}

ios/build/bots/chromium.fyi/ios12-sdk-xcode-clang.json

@@ -7,14 +7,13 @@
   "use xcode build version": true,
   "gn_args": [
     "additional_target_cpus=[\"x86\",\"arm64\",\"arm\"]",
-    "goma_dir=\"$(goma_dir)\"",
     "ios_enable_code_signing=false",
     "is_component_build=false",
     "is_debug=true",
     "symbol_level=1",
     "target_cpu=\"x64\"",
     "target_os=\"ios\"",
-    "use_goma=true",
+    "use_goma=false",
     "use_xcode_clang=true"
   ],
   "env": {