Revert of GrFP can express distance vector field req., program builder declares variable for it

src/gpu/GrPrimitiveProcessor.h

Index: src/gpu/GrPrimitiveProcessor.h
diff --git a/src/gpu/GrPrimitiveProcessor.h b/src/gpu/GrPrimitiveProcessor.h
index d27a6f31c78d67390f42c06fc4783175b79da6b1..0d5280fbd3ed44703d6a37068e5976f09cd4e547 100644
--- a/src/gpu/GrPrimitiveProcessor.h
+++ b/src/gpu/GrPrimitiveProcessor.h
@@ -221,10 +221,6 @@
         return 0.0;
     }
 
-    /* Sub-class should override and return true if this primitive processor implements the distance
-     * vector field, a field of vectors to the nearest point in the edge of the shape.  */
-    virtual bool implementsDistanceVector() const { return false; }
-
 protected:
     GrPrimitiveProcessor() : fVertexStride(0) {}