Bump iOS bots to iOS 11.

This should also solve the trigger problem on the iOS perf bot.

Remove device_type which appears to be ignored anyway. For instance,
device_type said iphone 6s but we got iPhone 8 when I actually looked
in the swarming dimension.

Bug: webrtc:7156
Change-Id: I1aa22e7f217deebf9eeee18363622e37ecc2a40e
Reviewed-on: https://webrtc-review.googlesource.com/99060
Commit-Queue: Patrik Höglund <phoglund@webrtc.org>
Reviewed-by: Oleh Prypin <oprypin@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#24648}

tools_webrtc/ios/internal.client.webrtc/iOS64_Debug.json

@@ -21,8 +21,7 @@
   "tests": [
     {
       "include": "real_device_tests.json",
-      "device type": "iPhone 6s",
+      "os": "11.4.1",
-      "os": "10.3.3",
       "dimensions": [
         {
           "os": "Mac",

tools_webrtc/ios/internal.client.webrtc/iOS64_Perf.json

@@ -21,8 +21,7 @@
   "tests": [
     {
       "include": "perf_tests.json",
-      "device type": "iPhone 7",
+      "os": "11.4.1",
-      "os": "11.0.3",
       "dimensions": [
         {
           "os": "Mac",

tools_webrtc/ios/internal.client.webrtc/iOS64_Release.json

@@ -22,8 +22,7 @@
   "tests": [
     {
       "include": "real_device_tests.json",
-      "device type": "iPhone 6s",
+      "os": "11.4.1",
-      "os": "10.3.3",
       "dimensions": [
         {
           "os": "Mac",