[C99] Remove WG14 N522 from the C status page

This paper is about type compatibility rules that changed in C99, but
this is only applicable across translation units and so there's nothing
for us to test. The specific change was that C89 allowed different tag
types (e.g., struct and union) to be compatible and C99 tightened that
restriction. This is a case where the user gets whatever they get if
they link two TUs with incompatible tag types.