entitymanager: drop duplicate header inclusion

Signed-off-by: Patrick Venture <venture@google.com>
Change-Id: I01531631bb32d824ee3064351dc7772f0a4599aa
diff --git a/src/EntityManager.cpp b/src/EntityManager.cpp
index 3e3e21b..17eeade 100644
--- a/src/EntityManager.cpp
+++ b/src/EntityManager.cpp
@@ -20,7 +20,6 @@
 
 #include <Overlay.hpp>
 #include <Utils.hpp>
-#include <VariantVisitors.hpp>
 #include <boost/algorithm/string/case_conv.hpp>
 #include <boost/algorithm/string/classification.hpp>
 #include <boost/algorithm/string/predicate.hpp>