Simplify gamma-correctness for text rendering.

Just use the DC flag, independent of the destination pixel config or the
special output override flag (which is only to be used internally be
special effects that will never hit this code path.)

BUG=skia:
GOLD_TRYBOT_URL= https://gold.skia.org/search2?unt=true&query=source_type%3Dgm&master=false&issue=1888473003

Review URL: https://codereview.chromium.org/1888473003
3 files changed