Flat map all the things

In an earlier commit, entity-manager gained required dependency
on std::flat_map.  This means that EM can only compile with gcc-15,
which the project only recently moved to.  Rather than move backwards,
port forward all uses of boost flat_map and flat_set to their std
equivalents.

Tested: entity-manager launches and enumerates devices on
gb200-obmc.

Change-Id: Id24803057711c60d5b00f436db80b27edbb756a3
Signed-off-by: Ed Tanous <etanous@nvidia.com>
diff --git a/src/entity_manager/perform_scan.hpp b/src/entity_manager/perform_scan.hpp
index 317177e..fc8382d 100644
--- a/src/entity_manager/perform_scan.hpp
+++ b/src/entity_manager/perform_scan.hpp
@@ -5,10 +5,10 @@
 
 #include <systemd/sd-journal.h>
 
-#include <boost/container/flat_map.hpp>
 #include <nlohmann/json.hpp>
 #include <sdbusplus/asio/object_server.hpp>
 
+#include <flat_map>
 #include <functional>
 #include <list>
 #include <vector>