[ios] Make dimension 'device_status' optional for clang_tot_device

Since there is only 1 device at the moment, skip the health check.

Bug: 723764
Cq-Include-Trybots: master.tryserver.chromium.mac:ios-simulator-cronet;master.tryserver.chromium.mac:ios-simulator-full-configs
Change-Id: Ic06468c2c0669413ce5507abdc0aeb3b2181ceb7
Reviewed-on: https://chromium-review.googlesource.com/1024299Reviewed-by: Sergey Berezin <sergeyberezin@chromium.org>
Commit-Queue: Justin Cohen <justincohen@chromium.org>
Cr-Commit-Position: refs/heads/master@{#552810}

ios/build/bots/chromium.clang/clang_tot_device.json

@@ -34,6 +34,7 @@
   },
   "configuration": "Release",
   "sdk": "iphoneos11.2",
+  "device check": false,
   "tests": [
     {
       "app": "base_unittests",