Make SkPixelRef::isLocked() debug-only, remove related dead code.

src/core/SkPixelRef.cpp

Index: src/core/SkPixelRef.cpp
diff --git a/src/core/SkPixelRef.cpp b/src/core/SkPixelRef.cpp
index f56298165cd67648276272f6667d9753c38b604e..c73c2f4b7dc3db2487a4d18e19b972d50b0a970f 100644
--- a/src/core/SkPixelRef.cpp
+++ b/src/core/SkPixelRef.cpp
@@ -197,14 +197,6 @@ bool SkPixelRef::onLockPixelsAreWritable() const {
     return true;
 }
 
-bool SkPixelRef::onImplementsDecodeInto() {
-    return false;
-}
-
-bool SkPixelRef::onDecodeInto(int pow2, SkBitmap* bitmap) {
-    return false;
-}
-
 uint32_t SkPixelRef::getGenerationID() const {
     if (0 == fGenerationID) {
         fGenerationID = SkNextPixelRefGenerationID();