Drop message severity

In the way we store the message registry, we store both Severity and
MessageSeverity.  Severity as a field is deprecated, and in every case
in every registry both fields have the same value.  We shouldn't
duplicate data in that way.  This commit changes the parse_registries.py
script to stop producing the Severity field into the struct.  The few
uses we have left are moved over to use MessageRegistry.

Tested:

Redfish service validator shows no errors on the
/redfish/v1/Registries tree.  Other errors present that were there
previously and are unchanged.

This saves a trivial amount: about 1kB on our compressed binary size.

Signed-off-by: Ed Tanous <edtanous@google.com>
Change-Id: Ibbaf533dc59eb08365d6ed309aba16b54bc40ca1
diff --git a/redfish-core/lib/message_registries.hpp b/redfish-core/lib/message_registries.hpp
index c0c6205..c030e5a 100644
--- a/redfish-core/lib/message_registries.hpp
+++ b/redfish-core/lib/message_registries.hpp
@@ -199,7 +199,7 @@
         nlohmann::json& obj = messageObj[message->first];
         obj = {{"Description", message->second.description},
                {"Message", message->second.message},
-               {"Severity", message->second.severity},
+               {"Severity", message->second.messageSeverity},
                {"MessageSeverity", message->second.messageSeverity},
                {"NumberOfArgs", message->second.numberOfArgs},
                {"Resolution", message->second.resolution}};