Rename shell namespace to service_manager

mash/login/main.cc

Index: mash/login/main.cc
diff --git a/mash/login/main.cc b/mash/login/main.cc
index 365f61ca5adb01d20010c3886f88654d3abf8b1b..e9fbf79e1ef6f4face70cb8892c48c1944b935ff 100644
--- a/mash/login/main.cc
+++ b/mash/login/main.cc
@@ -7,6 +7,6 @@
 #include "services/service_manager/public/cpp/service_runner.h"
 
 MojoResult ServiceMain(MojoHandle service_request_handle) {
-  shell::ServiceRunner runner(mash::login::CreateLogin());
+  service_manager::ServiceRunner runner(mash::login::CreateLogin());
   return runner.Run(service_request_handle);
 }