Use StartScan method in LorgnetteManagerClient

The implementation of StartScan now matches StartScanMultiPage in
Lorgnette. Convert LorgnetteManagerClient to use StartScan so that
StartScanMultiPage can be deleted.

Bug: b:161239919
Change-Id: Id3cd3bd7221aec461ade27cf3450f7f8fbf3fc98
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2427018Reviewed-by: Steven Bennetts <stevenjb@chromium.org>
Commit-Queue: Fletcher Woodruff <fletcherw@chromium.org>
Cr-Commit-Position: refs/heads/master@{#810728}

chromeos/dbus/lorgnette_manager_client.cc

@@ -80,7 +80,7 @@ class LorgnetteManagerClientImpl : public LorgnetteManagerClient {
     request.mutable_settings()->set_allocated_source(&source);
 
     dbus::MethodCall method_call(lorgnette::kManagerServiceInterface,
-                                 lorgnette::kStartScanMultiPageMethod);
+                                 lorgnette::kStartScanMethod);
     dbus::MessageWriter writer(&method_call);
     if (!writer.AppendProtoAsArrayOfBytes(request)) {
       LOG(ERROR) << "Failed to encode StartScanRequest protobuf";