[Media Router] Remove the extension ID getter from MRMojoImpl

chrome/browser/media/router/mojo/media_router_mojo_impl.cc

Index: chrome/browser/media/router/mojo/media_router_mojo_impl.cc
diff --git a/chrome/browser/media/router/mojo/media_router_mojo_impl.cc b/chrome/browser/media/router/mojo/media_router_mojo_impl.cc
index ec8e696fa07aae9209983e207d7ff18119f3d302..d16ab98ef6696c7a24f30815e79451d740229303 100644
--- a/chrome/browser/media/router/mojo/media_router_mojo_impl.cc
+++ b/chrome/browser/media/router/mojo/media_router_mojo_impl.cc
@@ -221,11 +221,6 @@ void MediaRouterMojoImpl::OnRoutesUpdated(
   RemoveInvalidRouteControllers(routes);
 }
 
-const std::string& MediaRouterMojoImpl::media_route_provider_extension_id()
-    const {
-  return event_page_request_manager_->media_route_provider_extension_id();
-}
-
 void MediaRouterMojoImpl::RouteResponseReceived(
     const std::string& presentation_id,
     bool is_incognito,