replace various SFIO to stderr with C stdio

replace various SFIO to stderr with C stdio

While it is technically possible to replace the `sfstderr` stream with something
other than stderr or use an SFIO-specific format specifier (e.g. `%!`), nothing
in Graphviz permits this. Thus we know all these instances are actually just
doing basic output to stderr. By replacing them with C stdio, they are more
transparent to the compiler and can be implemented more efficiently.

Gitlab: #1998