Reland "Remove support for decoding to kIndex_8"

Original change's description:
> > Remove support for decoding to kIndex_8
> > 
> > Fix up callsites, and remove tests that no longer make sense.
> > 
> > Bug: skia:6828
> > Change-Id: I2548c4b7528b7b1be7412563156f27b52c9d4295
> > Reviewed-on: https://skia-review.googlesource.com/21664
> > Reviewed-by: Derek Sollenberger <djsollen@google.com>
> > Commit-Queue: Leon Scroggins <scroggo@google.com>
> 
> TBR=djsollen@google.com,scroggo@google.com
> 
> Change-Id: I1bc669441f250690884e75a9a61427fdf75c6907
> No-Presubmit: true
> No-Tree-Checks: true
> No-Try: true
> Bug: skia:6828
> Reviewed-on: https://skia-review.googlesource.com/22120
> Reviewed-by: Leon Scroggins <scroggo@google.com>
> Commit-Queue: Leon Scroggins <scroggo@google.com>

TBR=djsollen@google.com,scroggo@google.com

Bug: skia:6828
Change-Id: I36ff5a11c529d29e8adc95f43b8edc6fd1dbf5b8
Reviewed-on: https://skia-review.googlesource.com/22320
Reviewed-by: Leon Scroggins <scroggo@google.com>
Commit-Queue: Leon Scroggins <scroggo@google.com>
diff --git a/src/codec/SkJpegCodec.h b/src/codec/SkJpegCodec.h
index 0c2f4a1..2d6822e 100644
--- a/src/codec/SkJpegCodec.h
+++ b/src/codec/SkJpegCodec.h
@@ -45,7 +45,7 @@
      * Initiates the jpeg decode
      */
     Result onGetPixels(const SkImageInfo& dstInfo, void* dst, size_t dstRowBytes, const Options&,
-            SkPMColor*, int*, int*) override;
+            int*) override;
 
     bool onQueryYUV8(SkYUVSizeInfo* sizeInfo, SkYUVColorSpace* colorSpace) const override;
 
@@ -120,8 +120,8 @@
      * Scanline decoding.
      */
     SkSampler* getSampler(bool createIfNecessary) override;
-    Result onStartScanlineDecode(const SkImageInfo& dstInfo, const Options& options,
-            SkPMColor ctable[], int* ctableCount) override;
+    Result onStartScanlineDecode(const SkImageInfo& dstInfo,
+            const Options& options) override;
     int onGetScanlines(void* dst, int count, size_t rowBytes) override;
     bool onSkipScanlines(int count) override;