Revert "Use Skia's new simplified read/write pixels code paths"

This reverts commit 6d0559c0.

Reason for revert: Breaks ImageBitmapTest.AvoidGPUReadback on MSAN, e.g. https://logs.chromium.org/v/?s=chromium%2Fbb%2Fchromium.memory%2FLinux_MSan_Tests%2F9783%2F%2B%2Frecipes%2Fsteps%2Fwebkit_unit_tests%2F0%2Flogs%2FImageBitmapTest.AvoidGPUReadback%2F0

Original change's description:
> Use Skia's new simplified read/write pixels code paths
> 
> Bug: 826819
> Change-Id: Ia6eaca75fe43f9d9ec94f8fe644a44e8e7436675
> Reviewed-on: https://chromium-review.googlesource.com/1054520
> Reviewed-by: Robert Phillips <robertphillips@google.com>
> Commit-Queue: Brian Salomon <bsalomon@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#557943}

TBR=bsalomon@chromium.org,robertphillips@google.com

# Not skipping CQ checks because original CL landed > 1 day ago.

Bug: 826819
Change-Id: Ia4dca1186fbb79569672fbf5cdabd9657c702762
Reviewed-on: https://chromium-review.googlesource.com/1056847Reviewed-by: Timothy Loh <timloh@chromium.org>
Commit-Queue: Timothy Loh <timloh@chromium.org>
Cr-Commit-Position: refs/heads/master@{#558215}

skia/config/SkUserConfig.h

@@ -220,6 +220,11 @@ SK_API void SkDebugf_FileLine(const char* file, int line, bool fatal,
 #define SK_SUPPORT_LEGACY_SVG_ARC_TO
 #endif
 
+// Remove after M66 branch to use new read/writePixels implementations
+#ifndef SK_LEGACY_GPU_PIXEL_OPS
+#define SK_LEGACY_GPU_PIXEL_OPS
+#endif
+
 #ifndef SK_SUPPORT_LEGACY_YUV_COLORSPACE
 #define SK_SUPPORT_LEGACY_YUV_COLORSPACE
 #endif