Headless: Remove obsolete Mojo code and some other obsolete APIs

headless/lib/browser/headless_web_contents_impl.h

Index: headless/lib/browser/headless_web_contents_impl.h
diff --git a/headless/lib/browser/headless_web_contents_impl.h b/headless/lib/browser/headless_web_contents_impl.h
index 3ea0c7887f3b637c245678c828b60b3ef5032205..af9f1a25bb2744bdebe5a6fadb363963c27286da 100644
--- a/headless/lib/browser/headless_web_contents_impl.h
+++ b/headless/lib/browser/headless_web_contents_impl.h
@@ -57,9 +57,6 @@ class HEADLESS_EXPORT HeadlessWebContentsImpl
   void RemoveObserver(Observer* observer) override;
   HeadlessDevToolsTarget* GetDevToolsTarget() override;
   HeadlessTabSocket* GetHeadlessTabSocket() const override;
-  bool GetFrameTreeNodeIdForDevToolsAgentHostId(
-      const std::string& devtools_agent_host_id,
-      int* frame_tree_node_id) const override;
 
   // HeadlessDevToolsTarget implementation:
   bool AttachClient(HeadlessDevToolsClient* client) override;
@@ -116,10 +113,6 @@ class HEADLESS_EXPORT HeadlessWebContentsImpl
   void InitializeScreen(const gfx::Size& initial_size);
   using MojoService = HeadlessWebContents::Builder::MojoService;
 
-  std::unordered_map<content::RenderFrameHost*, std::string>
-      render_frame_host_to_devtools_agent_host_id_;
-  std::unordered_map<std::string, int> devtools_agent_id_to_frame_tree_node_id_;
-
   class Delegate;
   std::unique_ptr<Delegate> web_contents_delegate_;
   std::unique_ptr<HeadlessWindowTreeHost> window_tree_host_;