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

webrtc/build/ios/client.webrtc/iOS64_Release_(GN).json

Index: webrtc/build/ios/client.webrtc/iOS64_Release_(GN).json
diff --git a/webrtc/build/ios/client.webrtc/iOS64_Release_(GN).json b/webrtc/build/ios/client.webrtc/iOS64_Release_(GN).json
deleted file mode 100644
index 1f5b4a6bd7982b51edec6ff72fa1746e211e2b68..0000000000000000000000000000000000000000
--- a/webrtc/build/ios/client.webrtc/iOS64_Release_(GN).json
+++ /dev/null
@@ -1,34 +0,0 @@
-{
-  "owners": [
-    "kjellander"
-  ],
-  "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."
-  ],
-  "xcode version": "8.0",
-  "GYP_DEFINES": [
-    "use_goma=1",
-    "gomadir=$(goma_dir)",
-    "chromium_ios_signing=0",
-    "component=static_library",
-    "target_arch=arm64"
-  ],
-  "gn_args": [
-    "is_debug=false",
-    "target_os=\"ios\"",
-    "ios_enable_code_signing=false",
-    "is_component_build=false",
-    "use_goma=true",
-    "goma_dir=\"$(goma_dir)\"",
-    "target_cpu=\"arm64\""
-  ],
-  "mb_type": "gyp",
-  "compiler": "ninja",
-  "additional_compile_targets": [ "all" ],
-  "configuration": "Release",
-  "sdk": "iphoneos9.0",
-  "tests": [
-  ]
-}