Revert of sdf: use linear edge distance approximation for all gradient directions

src/core/SkDistanceFieldGen.cpp

Index: src/core/SkDistanceFieldGen.cpp
diff --git a/src/core/SkDistanceFieldGen.cpp b/src/core/SkDistanceFieldGen.cpp
index c147151c3b21def3fcef267e30b972b86593152c..30354e09f83cb783c49ee018af74b3d8e236b272 100755
--- a/src/core/SkDistanceFieldGen.cpp
+++ b/src/core/SkDistanceFieldGen.cpp
@@ -107,9 +107,6 @@
 // computes the distance to an edge given an edge normal vector and a pixel's alpha value
 // assumes that direction has been pre-normalized
 static float edge_distance(const SkPoint& direction, float alpha) {
-#if 1    // formula (1)
-    return 0.5f - alpha;
-#else    // formula (4)
     float dx = direction.fX;
     float dy = direction.fY;
     float distance;
@@ -146,7 +143,6 @@
     }
 
     return distance;
-#endif
 }
 
 static void init_distances(DFData* data, unsigned char* edges, int width, int height) {