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 fbbffd10aa7fb859b86476a5ddc0905a04ebc53f..93edc99d60de7d77285d06627ac7450f56c3ff65 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;
   std::string GetUntrustedDevToolsFrameIdForFrameTreeNodeId(
       int process_id,
       int frame_tree_node_id) const override;
@@ -112,10 +109,6 @@ 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_;