message: Remove legacy variant and variant_ns

Now that we no longer have users of the
sdbusplus::message::variant{,_ns} alias we can remove it from sdbusplus
altogether.

Tested:
    Ran through a unit test run

Change-Id: Ic50f807f6111ddc5b0433a592fd8b198a2e24fcb
Signed-off-by: William A. Kennington III <wak@google.com>
diff --git a/sdbusplus/message/types.hpp b/sdbusplus/message/types.hpp
index 5b3c8e9..6b4ddc8 100644
--- a/sdbusplus/message/types.hpp
+++ b/sdbusplus/message/types.hpp
@@ -18,11 +18,6 @@
 namespace message
 {
 
-namespace variant_ns = std;
-
-template <typename... Args>
-using variant = variant_ns::variant<Args...>;
-
 namespace types
 {