Revert "Use new Skia GPU read/write pixel code paths"

This reverts commit f17c70fe.

Reason for revert: 

It looks like this change:

slowed down the file___static_top_25_weather.html rasterize_and_record time on the AndroidOne (crbug.com/825594)

slowed down getImageData and putImageData for the HTML5 Canvas across the board (crbug.com/825585)

Bug: 825594
Bug: 825585

Original change's description:
> Use new Skia GPU read/write pixel code paths
> 
> Change-Id: I8ea66d1b3bb8db174deab690a0cdacc39cf81992
> Reviewed-on: https://chromium-review.googlesource.com/973267
> Reviewed-by: Robert Phillips <robertphillips@google.com>
> Commit-Queue: Brian Salomon <bsalomon@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#544777}

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

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

Change-Id: Icaee5a1afa55bc8aec4567687661dacef0ccf565
Reviewed-on: https://chromium-review.googlesource.com/980292Reviewed-by: Robert Phillips <robertphillips@google.com>
Commit-Queue: Robert Phillips <robertphillips@google.com>
Cr-Commit-Position: refs/heads/master@{#545787}

skia/config/SkUserConfig.h

@@ -208,6 +208,11 @@ 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