Remove some iOS 9 CQ configurations to reduce load.

ios/build/bots/chromium.mac/ios-simulator.json

Index: ios/build/bots/chromium.mac/ios-simulator.json
diff --git a/ios/build/bots/chromium.mac/ios-simulator.json b/ios/build/bots/chromium.mac/ios-simulator.json
index 95357ffdb685d8bfd6cfe3aea0e208fccdb9dc95..79d61520e2a69e33e09ca79242415b9ea4198b85 100644
--- a/ios/build/bots/chromium.mac/ios-simulator.json
+++ b/ios/build/bots/chromium.mac/ios-simulator.json
@@ -51,18 +51,6 @@
     },
     {
       "include": "common_tests.json",
-      "device type": "iPhone 6s Plus",
-      "os": "9.0",
-      "xcode version": "8.0"
-    },
-    {
-      "include": "common_tests.json",
-      "device type": "iPhone 6s",

[rohitrao (ping after 24h), 2017/05/05 11:26:55]

This is probably our most popular iOS9 configuration, so I'm the most concerned
about dropping this one.

[baxley, 2017/05/05 13:22:18]

Okay, I see two options...
1. Drop iPhone 5 and iPad Air 2 on iOS 9 (keeping iPhone 6s and iPad Retina).
2. Simply keep iPhone 6s, only removing 2 out of the 10 configs.

I'd lean towards 1, but am open if there's a compelling reason to keep iPad Air
2 or iPhone 5 on iOS 9.

-      "os": "9.0",
-      "xcode version": "8.0"
-    },
-    {
-      "include": "common_tests.json",
       "device type": "iPhone 5",
       "os": "9.0",
       "xcode version": "8.0"
@@ -72,12 +60,6 @@
       "device type": "iPad Air 2",
       "os": "9.0",
       "xcode version": "8.0"
-    },
-    {
-      "include": "common_tests.json",
-      "device type": "iPad Retina",
-      "os": "9.0",
-      "xcode version": "8.0"
     }
   ]
 }