Change message_registries namespace to registries

The message_registries namespace is overly wordy, and results in very
long defines.  Doing this one minor change reduces the code by 50 lines.
This seems worthwhile.

Tested: Unit tests pass.  Namespace change only.

Signed-off-by: Ed Tanous <edtanous@google.com>
Change-Id: Ib1401580b3fa47596eb56cdc86e60eeeb1c2f952
diff --git a/redfish-core/include/registries.hpp b/redfish-core/include/registries.hpp
index f85d2a5..eff91a4 100644
--- a/redfish-core/include/registries.hpp
+++ b/redfish-core/include/registries.hpp
@@ -19,7 +19,7 @@
 #include <string>
 #include <string_view>
 
-namespace redfish::message_registries
+namespace redfish::registries
 {
 struct Header
 {
@@ -62,4 +62,4 @@
     }
 }
 
-} // namespace redfish::message_registries
+} // namespace redfish::registries