Revert "Bump stored lowp uniform color to 16-bit storage."

This reverts commit d286bfbd96f8b7ccf1cbce74f07d2f3917dbec30.

Reason for revert:

../../../src/core/SkRasterPipeline.cpp:98:34: runtime error: 4.87906e+09 is outside the range of representable values of type 'unsigned short'

Excellent new bot!

Original change's description:
> Bump stored lowp uniform color to 16-bit storage.
> 
> This makes loading into 16-bit channels more natural in _lowp.cpp.
> 
> Change-Id: I1ed393873654060ef52f4632d670465528006bbd
> Reviewed-on: https://skia-review.googlesource.com/47261
> Reviewed-by: Mike Reed <reed@google.com>
> Commit-Queue: Mike Klein <mtklein@chromium.org>

TBR=mtklein@chromium.org,reed@google.com

Change-Id: Ia65645c1261a7b31588c4ddaf2b1b3b327d265b0
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Reviewed-on: https://skia-review.googlesource.com/47540
Reviewed-by: Mike Klein <mtklein@google.com>
Commit-Queue: Mike Klein <mtklein@google.com>
5 files changed