SkPDF: Use Pathops clipping

Turn this on all the time.  Remove the SK_PDF_USE_PATHOPS_CLIPPING
define that used to hide this functionality.

All rendering tests are the same or improved by this.

Also, remove non-functional SK_ALLOW_LARGE_PDF_SCALARS.

TBR=reed@google.com
    removing dead #defines from SkUserConfig.h

BUG=591805
GOLD_TRYBOT_URL= https://gold.skia.org/search2?unt=true&query=source_type%3Dgm&master=false&issue=1845623002

Review URL: https://codereview.chromium.org/1845623002