Remove render thread created callbacks (see issue #2498)

With site-per-process enabled a spare renderer process will be created
for use with a future browser or navigation. Consequently the
|extra_info| parameter populated in OnRenderProcessThreadCreated will no
longer be delivered to OnRenderThreadCreated in the expected renderer
process. To avoid confusion these callbacks have been removed completely.

After this change CefRenderProcessHandler::OnWebKitInitialized should
be used for startup tasks in the render process, and OnBrowserCreated
should be used in the render process to recieve |extra_info| passed from
CefBrowserHost::CreateBrowser or CefLifeSpanHandler::OnBeforePopup.

include/capi/cef_browser_process_handler_capi.h

@@ -33,7 +33,7 @@
 // by hand. See the translator.README.txt file in the tools directory for
 // more information.
 //
-// $hash=b15ba2c750f5227b6b40fea59965817ba4431ee0$
+// $hash=306236316b35037523ca566068d133755bce48fd$
 //
 
 #ifndef CEF_INCLUDE_CAPI_CEF_BROWSER_PROCESS_HANDLER_CAPI_H_
@@ -78,17 +78,6 @@ typedef struct _cef_browser_process_handler_t {
       struct _cef_browser_process_handler_t* self,
       struct _cef_command_line_t* command_line);
 
-  ///
-  // Called on the browser process IO thread after the main thread has been
-  // created for a new render process. Provides an opportunity to specify extra
-  // information that will be passed to
-  // cef_render_process_handler_t::on_render_thread_created() in the render
-  // process. Do not keep a reference to |extra_info| outside of this function.
-  ///
-  void(CEF_CALLBACK* on_render_process_thread_created)(
-      struct _cef_browser_process_handler_t* self,
-      struct _cef_list_value_t* extra_info);
-
   ///
   // Return the handler for printing on Linux. If a print handler is not
   // provided then printing will not be supported on the Linux platform.