readme: remove outdated helper

Peter's hint to use functools.partial() for the render params does not
apply anymore - we actually need to use a global variable to transfer
things only once.

For reference, the old (and embarrassing) python discuss thread was
15113.

README.md

@@ -843,7 +843,6 @@ This results in pypdfium2 being part of a large dependency tree.
 * [Adam Huganir](https://github.com/adam-huganir): Help with maintenance and development decisions since the beginning of the project.
 * [kobaltcore](https://github.com/kobaltcore): Bug fix for `PdfDocument.save()`.
 * [Mike Kroutikov](https://github.com/mkroutikov): Examples on how to use PDFium with ctypes in `redstork` and `pdfbrain`.
-* [Peter Saalbrink](https://github.com/petersaalbrink): Code style improvements to the multipage renderer.
 
 ... and further [code contributors](https://github.com/pypdfium2-team/pypdfium2/graphs/contributors) (GitHub stats).