Remove support for MetroWerks CodeWarrior compiler.

This compiler doesn't exist any more and was probably unsupported even in 2.8,
let alone 2.9, so remove all the __MWERKS__ tests to simplify things.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@71102 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

src/common/variant.cpp

@@ -37,11 +37,6 @@
     #endif
 #endif
 
-#if defined(__MWERKS__) && __MSL__ >= 0x6000
-namespace std {}
-using namespace std ;
-#endif
-
 #if wxUSE_STREAMS
     #include "wx/txtstrm.h"
 #endif