Replace std::tr1::shared_ptr by std::shared_ptr.

This patch replaces C++ Technical Report 1 additions to C++03 with
the newer C++11 name.

Includes and using statements updated accordingly.

BUG=None
TEST=Build and unittests.

Change-Id: I9bdad6d39684545c786f5c76fb598a15b557d6eb
Reviewed-on: https://chromium-review.googlesource.com/200665
Tested-by: Alex Deymo <deymo@chromium.org>
Reviewed-by: David Zeuthen <zeuthen@chromium.org>
Commit-Queue: Alex Deymo <deymo@chromium.org>
diff --git a/subprocess.cc b/subprocess.cc
index 7021cc5..5274655 100644
--- a/subprocess.cc
+++ b/subprocess.cc
@@ -18,8 +18,8 @@
 
 #include "update_engine/utils.h"
 
+using std::shared_ptr;
 using std::string;
-using std::tr1::shared_ptr;
 using std::vector;
 
 namespace chromeos_update_engine {