Remove arithmetic mode GrXP code.

The arithmetic mode xfermode is only used as an implementation detail of SkXfermodeImageFilter which always uses the arithmetic FP.

Change-Id: I5f9607aa9731a21e6666d9c749dfa705d40d5775
Reviewed-on: https://skia-review.googlesource.com/6688
Commit-Queue: Brian Salomon <bsalomon@google.com>
Reviewed-by: Greg Daniel <egdaniel@google.com>
diff --git a/src/gpu/GrProcessor.cpp b/src/gpu/GrProcessor.cpp
index f4f7ccb..991aa90 100644
--- a/src/gpu/GrProcessor.cpp
+++ b/src/gpu/GrProcessor.cpp
@@ -52,7 +52,7 @@
  */
 static const int kFPFactoryCount = 40;
 static const int kGPFactoryCount = 14;
-static const int kXPFactoryCount = 5;
+static const int kXPFactoryCount = 4;
 
 template<>
 void GrProcessorTestFactory<GrFragmentProcessor>::VerifyFactoryCount() {