[WebOTP] Remove obsolete comment

The patch was landed and `NOTIMPLEMENTED` has been updated to
`NOTREACHED`.

TBR=majidvp@chromium.org

Change-Id: I8f147db129878cc3f3c211c703931329a750fcf0
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2551495Reviewed-by: Yi Gu <yigu@chromium.org>
Commit-Queue: Yi Gu <yigu@chromium.org>
Cr-Commit-Position: refs/heads/master@{#829479}

content/browser/sms/webotp_service.cc

@@ -179,7 +179,6 @@ void WebOTPService::OnFailure(FailureType failure_type) {
       break;
     case FailureType::kPromptTimeout:
     case FailureType::kPromptCancelled:
-      // TODO(yigu): Land implementation in crrev.com/2427560.
       NOTREACHED();
       break;
   }