headless: Remove old load observer API

headless/lib/browser/headless_web_contents_impl.cc

Index: headless/lib/browser/headless_web_contents_impl.cc
diff --git a/headless/lib/browser/headless_web_contents_impl.cc b/headless/lib/browser/headless_web_contents_impl.cc
index 723032a83216f5b114e4e99bcc38c87cf15c2c0d..13ed5e1076c6626517f1e329687d6b4678a92286 100644
--- a/headless/lib/browser/headless_web_contents_impl.cc
+++ b/headless/lib/browser/headless_web_contents_impl.cc
@@ -39,16 +39,6 @@ class WebContentsObserverAdapter : public content::WebContentsObserver {
     observer_->DevToolsTargetReady();
   }
 
-  void DocumentOnLoadCompletedInMainFrame() override {
-    observer_->DocumentOnLoadCompletedInMainFrame();
-  }
-
-  void DidFinishNavigation(
-      content::NavigationHandle* navigation_handle) override {
-    observer_->DidFinishNavigation(navigation_handle->HasCommitted() &&
-                                   !navigation_handle->IsErrorPage());
-  }
-
  private:
   HeadlessWebContents::Observer* observer_;  // Not owned.