Remove the project generator support for Visual Studio 6.0, .Net (2002) and 2003. This support is unmaintained for quite some time and these compilers and their C libraries are not even supported by Microsoft anymore.
* build/generator/gen_msvc_dsp.py Remove file.
* build/generator/gen_vcnet_vcproj.py (get_external_project): Remove function; falling back to ancestor.
* build/generator/gen_win.py (get_external_project): Remove serf project hack that wasn't used since 1.7.