Clean up unflattening paints

Just removing legacy cruft for fonts, and also change to return by
value (cleaner).

Change-Id: If120931119c32542e06801da2b6d60ba84ba2186
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/437676
Reviewed-by: Florin Malita <fmalita@chromium.org>
Commit-Queue: Mike Reed <reed@google.com>
8 files changed