Make mojo_system static and mojo_system_impl a component, never use both

mojo/shell/app_child_process.cc

Index: mojo/shell/app_child_process.cc
diff --git a/mojo/shell/app_child_process.cc b/mojo/shell/app_child_process.cc
index 7909d83da23d502a4891c9662e6e58cb1ff64cfc..d17fe05afb20edce4b2369009bcc6c39043cd871 100644
--- a/mojo/shell/app_child_process.cc
+++ b/mojo/shell/app_child_process.cc
@@ -91,9 +91,6 @@ class AppContext {
   ~AppContext() {}
 
   void Init() {
-    // Initialize Mojo before starting any threads.
-    embedder::Init();
-
     // Create and start our I/O thread.
     base::Thread::Options io_thread_options(base::MessageLoop::TYPE_IO, 0);
     CHECK(io_thread_.StartWithOptions(io_thread_options));