Delete SkBitmapRegionCanvas

This was an approach we considered for implementing Android's
BitmapRegionDecoder.

It was useful for testing and comparison, but now is no longer worth
maintaining and testing.

The approach to subset/scaled decodes (clipped decode, then scale)
may be worth reconsidering at some point.

BUG=skia:5307
GOLD_TRYBOT_URL= https://gold.skia.org/search2?unt=true&query=source_type%3Dgm&master=false&issue=1990543002

Review-Url: https://codereview.chromium.org/1990543002
diff --git a/dm/DMSrcSink.h b/dm/DMSrcSink.h
index b486642..b0f67db 100644
--- a/dm/DMSrcSink.h
+++ b/dm/DMSrcSink.h
@@ -165,7 +165,7 @@
         kDivisor_Mode,
     };
 
-    BRDSrc(Path, SkBitmapRegionDecoder::Strategy, Mode, CodecSrc::DstColorType, uint32_t);
+    BRDSrc(Path, Mode, CodecSrc::DstColorType, uint32_t);
 
     Error draw(SkCanvas*) const override;
     SkISize size() const override;
@@ -173,7 +173,6 @@
     bool veto(SinkFlags) const override;
 private:
     Path                                     fPath;
-    SkBitmapRegionDecoder::Strategy          fStrategy;
     Mode                                     fMode;
     CodecSrc::DstColorType                   fDstColorType;
     uint32_t                                 fSampleSize;