Rename SMSReceiverOutcome to WebOTPServiceOutcome in UKM.

SMSReceiverOutcome was renamed to WebOTPServiceOutcome in
https://chromium-review.googlesource.com/c/chromium/src/+/2424707
Fix the enum name in UKM.xml


TBR=rkaplow@chromium.org,swapnilgupta@google.com

Bug: 1138180
Change-Id: Ieb6e540eed2a88c8421c2e1f93abef51ee69d6d9
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2470565Reviewed-by: Illia Klimov <elklm@google.com>
Reviewed-by: Swapnil Gupta <swapnilgupta@google.com>
Commit-Queue: Illia Klimov <elklm@google.com>
Cr-Commit-Position: refs/heads/master@{#816980}

tools/metrics/ukm/ukm.xml

@@ -11481,7 +11481,7 @@ be describing additional metrics about the same event.
   <summary>
     Records performance metrics for SMSReceiver API.
   </summary>
-  <metric name="Outcome" enum="SMSReceiverOutcome">
+  <metric name="Outcome" enum="WebOTPServiceOutcome">
     <summary>
       Records the result of a call to the SmsReceiver API.
     </summary>