move SkScalarLog2 into its only client, in a move to reduce our public API surface area

include/core/SkScalar.h

Index: include/core/SkScalar.h
diff --git a/include/core/SkScalar.h b/include/core/SkScalar.h
index 93677df06908f58027dc6cc14d37545e5ee2b30e..4ab361604ff5260e8b2dcb2163c6bce2ccddd84a 100644
--- a/include/core/SkScalar.h
+++ b/include/core/SkScalar.h
@@ -216,12 +216,6 @@ static inline SkScalar SkScalarInterp(SkScalar A, SkScalar B, SkScalar t) {
     return A + SkScalarMul(B - A, t);
 }
 
-static inline SkScalar SkScalarLog2(SkScalar x) {
-    static const SkScalar log2_conversion_factor = SkScalarDiv(1, SkScalarLog(2));
-
-    return SkScalarMul(SkScalarLog(x), log2_conversion_factor);
-}
-
 /** Interpolate along the function described by (keys[length], values[length])
     for the passed searchKey.  SearchKeys outside the range keys[0]-keys[Length]
     clamp to the min or max value.  This function was inspired by a desire