iOS: Cleanup buildbot JSON files + bump iOS version to 10.0

webrtc/build/ios/tryserver.webrtc/ios_arm64_dbg.json

Index: webrtc/build/ios/tryserver.webrtc/ios_arm64_dbg.json
diff --git a/webrtc/build/ios/tryserver.webrtc/ios_arm64_dbg.json b/webrtc/build/ios/tryserver.webrtc/ios_arm64_dbg.json
index e23da1fdc2fa3f0c8740293d94d3e2734c4c4a0f..f4c605cb7c1faca43a0573881be9d76a350691c7 100644
--- a/webrtc/build/ios/tryserver.webrtc/ios_arm64_dbg.json
+++ b/webrtc/build/ios/tryserver.webrtc/ios_arm64_dbg.json
@@ -4,32 +4,19 @@
   ],
   "comments": [
     "Builder for 64-bit devices.",
-    "GYP_DEFINES and gn_args in this file are only used during runhooks; ",
-    "webrtc/build/mb_config.pyl decides the generated projects that are compiled."
+    "gn_args in this file is only read by the buildbot recipe; ",
+    "webrtc/build/mb_config.pyl contains the actual build configuration.",
+    "TODO(kjellander): remove gn_args when the recipe is updated."
   ],
   "xcode version": "8.0",
-  "GYP_DEFINES": [
-    "use_goma=1",
-    "gomadir=$(goma_dir)",
-    "chromium_ios_signing=0",
-    "component=static_library",
-    "target_arch=arm64"
-  ],
   "gn_args": [
-    "is_debug=true",
-    "target_os=\"ios\"",
-    "ios_enable_code_signing=false",
-    "is_component_build=false",
-    "use_goma=true",
-    "goma_dir=\"$(goma_dir)\"",
-    "target_cpu=\"arm64\""
+    "use_goma=true"
   ],
   "use_analyze": false,
-  "mb_type": "gn",
   "compiler": "ninja",
   "additional_compile_targets": [ "all" ],
   "configuration": "Debug",
-  "sdk": "iphoneos9.0",
+  "sdk": "iphoneos10.0",
   "tests": [
   ]
 }