Revert "Add support for unpremul image sources in the GPU backend"

This reverts commit f06240de2c4583c8d8ef2e798dd4636e6cfe8f47.

Reason for revert: I think this requires the skcms codec change to re-land,

Original change's description:
> Add support for unpremul image sources in the GPU backend
> 
> Change-Id: Ib940fa0d658fff0b2dd923abfcc5ca4a49b2b38b
> Reviewed-on: https://skia-review.googlesource.com/148397
> Commit-Queue: Brian Osman <brianosman@google.com>
> Reviewed-by: Mike Klein <mtklein@google.com>

TBR=mtklein@google.com,bsalomon@google.com,brianosman@google.com

Change-Id: Ib9358cf858c3c0887322503a4b021e08a0ac4cd5
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Reviewed-on: https://skia-review.googlesource.com/148861
Reviewed-by: Brian Osman <brianosman@google.com>
Commit-Queue: Brian Osman <brianosman@google.com>
diff --git a/src/gpu/GrYUVProvider.cpp b/src/gpu/GrYUVProvider.cpp
index 9ffd8a7..3c6c7f7 100644
--- a/src/gpu/GrYUVProvider.cpp
+++ b/src/gpu/GrYUVProvider.cpp
@@ -130,7 +130,7 @@
     // If the caller expects the pixels in a different color space than the one from the image,
     // apply a color conversion to do this.
     std::unique_ptr<GrFragmentProcessor> colorConversionProcessor =
-            GrColorSpaceXformEffect::Make(srcColorSpace, kPremul_SkAlphaType, dstColorSpace);
+            GrColorSpaceXformEffect::Make(srcColorSpace, dstColorSpace);
     if (colorConversionProcessor) {
         paint.addColorFragmentProcessor(std::move(colorConversionProcessor));
     }