remove 565 effects shaders

This removes the 565 optimization for radial,
linear, sweep, and picture shaders. The
optimization gets little real-world use and
has a reasonable fallback. This also permits
removing the square root table for the radial
gradient case.

R=reed@google.com
BUG=skia:1947
GOLD_TRYBOT_URL= https://gold.skia.org/search2?unt=true&query=source_type%3Dgm&master=false&issue=1553103003

Review URL: https://codereview.chromium.org/1553103003
14 files changed