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

docs/doxygen/mainpages/const_wxusedef.h

@@ -350,8 +350,8 @@ manifest from wxWidgets RC file. See also wxUSE_RC_MANIFEST.}
 @itemdef{wxUSE_POSTSCRIPT_ARCHITECTURE_IN_MSW, Use PS printing in wxMSW.}
 @itemdef{wxUSE_PS_PRINTING, See src/msw/dcprint.cpp file.}
 @itemdef{wxUSE_RC_MANIFEST, Include manifest for common controls library v6
-from wxWidgets RC file. This may be needed to be defined explicitly for MSVC 6
-and 7 (98 and 2003) only as later versions of MSVC generate this manifest
+from wxWidgets RC file. This may be needed to be defined explicitly for MSVC 7
+(a.k.a. MSVS 2003) only as later versions of MSVC generate this manifest
 themselves and the manifest generation is enabled by default for the other
 compilers. See also wxUSE_NO_MANIFEST.}
 @itemdef{wxUSE_REGKEY, Use wxRegKey class.}