Diagnostics: Remove unnecessary div from cards

- Unnecessary because the "title" slot can be placed directly
  on the div that contains the title text content for the
  card.

Bug: 1125150
Test: browser_tests --gtest_filter=DiagnosticsApp*
Change-Id: I4f5620c6c07d5afc28288fd04dd902ca5f92dc0e
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2443499
Commit-Queue: Michael Checo <michaelcheco@google.com>
Reviewed-by: Zentaro Kavanagh <zentaro@chromium.org>
Cr-Commit-Position: refs/heads/master@{#813383}

chromeos/components/diagnostics_ui/resources/battery_status_card.html

@@ -2,9 +2,7 @@
 </style>
 
 <diagnostics-card>
-  <div slot="title">
-    <div id="cardTitle">[[i18n('batteryTitle')]]</div>
-  </div>
+  <div id="cardTitle" slot="title">[[i18n('batteryTitle')]]</div>
   <data-point slot="body" id="currentNow"
     value="[[batteryChargeStatus_.current_now_milliamps]]">
   </data-point>

chromeos/components/diagnostics_ui/resources/cpu_card.html

@@ -2,9 +2,7 @@
 </style>
 
 <diagnostics-card>
-  <div slot="title">
-    <div id="cardTitle">[[i18n('cpuTitle')]]</div>
-  </div>
+  <div id="cardTitle" slot="title">[[i18n('cpuTitle')]]</div>
   <!-- TODO(michaelcheco): Add i18n string for percent number format -->
   <data-point slot="body" id="cpuUsageUser"
     value="[[computeCurrentlyUsing_(cpuUsage_.percent_usage_system,

chromeos/components/diagnostics_ui/resources/memory_card.html

@@ -2,9 +2,7 @@
 </style>
 
 <diagnostics-card>
-  <div slot="title">
-    <div id="cardTitle">[[i18n('memoryTitle')]]</div>
-  </div>
+  <div id="cardTitle" slot="title">[[i18n('memoryTitle')]]</div>
   <data-point slot="body" id="memoryTotal"
     value="[[memoryUsage_.total_memory_kib]]">
   </data-point>