remove SK_IGNORE_TO_STRING

SK_IGNORE_TO_STRING is not defined anywhere.
The same effect can be had by using a modern
linker.

Removing it simplifies bookmaker and makes
our includes easier to understand.

R=robertphillips@google.com
TBR=reed@google.com

Bug: skia:6898
Change-Id: Ib716f5ef1b42a7fbda0df43ece212d1b7c40289f
Reviewed-on: https://skia-review.googlesource.com/118963
Reviewed-by: Robert Phillips <robertphillips@google.com>
Reviewed-by: Cary Clark <caryclark@skia.org>
Commit-Queue: Cary Clark <caryclark@skia.org>
diff --git a/src/shaders/gradients/SkLinearGradient.cpp b/src/shaders/gradients/SkLinearGradient.cpp
index 21338b8..b6436ca 100644
--- a/src/shaders/gradients/SkLinearGradient.cpp
+++ b/src/shaders/gradients/SkLinearGradient.cpp
@@ -214,7 +214,6 @@
 
 #endif
 
-#ifndef SK_IGNORE_TO_STRING
 void SkLinearGradient::toString(SkString* str) const {
     str->append("SkLinearGradient (");
 
@@ -225,4 +224,4 @@
 
     str->append(")");
 }
-#endif
+