While fixing #14470 to remove w9xpopen support, removing it from old Visual Studio projects came up.

1. I can't imagine anyone is attempting to use most of these.
2. Since we don't backport build changes to these older versions, some of them are very out of date and can't be that useful.

I propose to remove the following:
1. PC/VC6 - this version is from 1998 and is the last compiler to support Win9x, which we just removed support for with the w9xpopen change via PEP 11.
2. PC/VS7.1 - this version is from 2003 and still contains references to WISE installer, which IIRC has not been used since 2.3. On top of that, it's missing many of the current project files.

I'm skeptical of PC/VS8.0's use as Visual Studio 2005 is pretty old and it too is missing many current project files, but there is a conversion script that may help point someone in the right direction. I do remember Hirokazu Yamamoto mentioning using 2005 for some purposes, but this was years ago.