Implement Physical Web listener registration

ios/chrome/common/physical_web/ios_chrome_physical_web_data_source.mm

Index: ios/chrome/common/physical_web/ios_chrome_physical_web_data_source.mm
diff --git a/ios/chrome/common/physical_web/ios_chrome_physical_web_data_source.mm b/ios/chrome/common/physical_web/ios_chrome_physical_web_data_source.mm
index 0d4f70a0165637f49d2ac3da1962c68eb22270c3..41ce75763a7144104d88c660a349203692f862c8 100644
--- a/ios/chrome/common/physical_web/ios_chrome_physical_web_data_source.mm
+++ b/ios/chrome/common/physical_web/ios_chrome_physical_web_data_source.mm
@@ -45,9 +45,3 @@ std::unique_ptr<base::ListValue> IOSChromePhysicalWebDataSource::GetMetadata() {
 bool IOSChromePhysicalWebDataSource::HasUnresolvedDiscoveries() {
   return [scanner_ unresolvedBeaconsCount] > 0;
 }
-
-void IOSChromePhysicalWebDataSource::RegisterListener(
-    PhysicalWebListener* physical_web_listener) {}
-
-void IOSChromePhysicalWebDataSource::UnregisterListener(
-    PhysicalWebListener* physical_web_listener) {}