Removes the "pdf_use_skia_paths" GN arg, and any other remaining
references to SkiaPaths.

Fixed: pdfium:1941
Change-Id: Ie46d84067277979d750265ae48ffd86ca90e035a
Reviewed-on: https://pdfium-review.googlesource.com/c/pdfium/+/101811
Reviewed-by: Nigi <nigi@chromium.org>
Commit-Queue: K. Moon <kmoon@chromium.org>