Revert of Make SkPicture/SkImageGenerator default to SkCodec

tests/KtxTest.cpp

Index: tests/KtxTest.cpp
diff --git a/tests/KtxTest.cpp b/tests/KtxTest.cpp
index 99bae83329a7c802443217d107aa4dcf79b313fd..84d162c0f83a103582b1e5d26384e4203f309dfa 100644
--- a/tests/KtxTest.cpp
+++ b/tests/KtxTest.cpp
@@ -143,9 +143,6 @@
     }
 }
 
-// For KtxReexportPKM, below. Defined in SkImageDecoder_ktx.cpp
-extern SkImageGenerator* decoder_image_generator(SkData*);
-
 /**
  * Finally, make sure that if we get ETC1 data from a PKM file that we can then
  * accurately write it out into a KTX file (i.e. transferring the ETC1 data from
@@ -163,7 +160,7 @@
     }
 
     bool installDiscardablePixelRefSuccess =
-        SkDEPRECATED_InstallDiscardablePixelRef(decoder_image_generator(fileData), &etcBitmap);
+        SkDEPRECATED_InstallDiscardablePixelRef(fileData, &etcBitmap);
     if (!installDiscardablePixelRefSuccess) {
         ERRORF(reporter, "failed to create discardable pixelRef from KTX file");
         return;