Remove some linear-blending sRGB logic from sk_app

Leftover logic from when viewer tried to use an sRGB FBO0
when rendering to a surface with a color space attached.

Most of this had already been removed, found a few more bits.

Change-Id: I998a541f75ecc184d218d02e24ab57657e096f22
Reviewed-on: https://skia-review.googlesource.com/139764
Auto-Submit: Brian Osman <brianosman@google.com>
Commit-Queue: Mike Klein <mtklein@chromium.org>
Reviewed-by: Mike Klein <mtklein@chromium.org>
3 files changed