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/ut/registries_test.cpp b/redfish-core/ut/registries_test.cpp
index 8340340..b75883c 100644
--- a/redfish-core/ut/registries_test.cpp
+++ b/redfish-core/ut/registries_test.cpp
@@ -4,7 +4,7 @@
 
 TEST(RedfishRegistries, fillMessageArgs)
 {
-    using redfish::message_registries::fillMessageArgs;
+    using redfish::registries::fillMessageArgs;
     std::string toFill("%1");
     fillMessageArgs({{"foo"}}, toFill);
     EXPECT_EQ(toFill, "foo");