Wi-Fi Sync: Fix histogram name.

This change updates the Wi-Fi Sync feature state histogram
from MultiDevice.WifiSync.MultiDeviceFeatureState to
WifiSync.MultiDeviceFeatureState in order to match the
name used when it's recorded.

Change-Id: Id079254eaae01ec2f571e6628035f32cc2973677
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2728491
Reviewed-by: Ilya Sherman <isherman@chromium.org>
Commit-Queue: Jon Mann <jonmann@chromium.org>
Cr-Commit-Position: refs/heads/master@{#859552}

tools/metrics/histograms/histograms_xml/multi_device/histograms.xml

@@ -409,8 +409,8 @@ reviews. Googlers can read more about this at go/gwsq-gerrit.
   </summary>
 </histogram>
 
-<histogram name="MultiDevice.WifiSync.MultiDeviceFeatureState"
-    enum="MultiDevice_FeatureState" expires_after="2021-09-01">
+<histogram name="WifiSync.MultiDeviceFeatureState"
+    enum="MultiDevice_FeatureState" expires_after="2022-03-01">
   <owner>cvandermerwe@google.com</owner>
   <owner>better-together-dev@google.com</owner>
   <summary>