health: remove boost container header

This header is not used.

Tested: compiles.

Signed-off-by: Nan Zhou <nanzhoumails@gmail.com>
Change-Id: Icb07db21b10b99c068eb93529136fe444819908a
diff --git a/redfish-core/lib/health.hpp b/redfish-core/lib/health.hpp
index c7f2960..04281bf 100644
--- a/redfish-core/lib/health.hpp
+++ b/redfish-core/lib/health.hpp
@@ -19,7 +19,6 @@
 
 #include <app.hpp>
 #include <boost/algorithm/string/predicate.hpp>
-#include <boost/container/flat_set.hpp>
 #include <dbus_singleton.hpp>
 #include <dbus_utility.hpp>
 #include <nlohmann/json.hpp>