Remove MSVC6 support.

Don't support this compiler any more, this allows to get rid of tons of
MSVC6-specific workarounds, in particular we can now use Bind() and natural
template functions calls in the library code.

Also remove MSVC6 project and solution files and don't generate them when
bakefile_gen is ran any more (removing the remaining occurrences of msvc6prj
from the bakefiles results in weird bake-time errors, so it's simpler to just
leave them there).

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@76532 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

include/wx/compiler.h

@@ -35,12 +35,8 @@
       define special symbols for different VC version instead of writing tests
       for magic numbers such as 1200, 1300 &c repeatedly
     */
-#if __VISUALC__ < 1100
-#   error "This Visual C++ version is too old and not supported any longer."
-#elif __VISUALC__ < 1200
-#   define __VISUALC5__
-#elif __VISUALC__ < 1300
-#   define __VISUALC6__
+#if __VISUALC__ < 1300
+#   error "This Visual C++ version is not supported any longer (at least MSVC 2003 required)."
 #elif __VISUALC__ < 1400
 #   define __VISUALC7__
 #elif __VISUALC__ < 1500