Revert "clamp to premul when reading premul sRGB"

This reverts commit 04e10da8362a0dcabd795a4ad53f617719ca0d20.

Reason for revert: roll?

Change-Id: Id0a8dcd62763bd6eddde120c513ca97e098a4268
Reviewed-on: https://skia-review.googlesource.com/6022
Commit-Queue: Mike Klein <mtklein@chromium.org>
Reviewed-by: Mike Klein <mtklein@chromium.org>
7 files changed