replace arcto quads with a conic

also, remove code used only for
the quad generation

R=reed@google.com
BUG=578885
GOLD_TRYBOT_URL= https://gold.skia.org/search2?unt=true&query=source_type%3Dgm&master=false&issue=1612543003

Review URL: https://codereview.chromium.org/1612543003
4 files changed