Remove canApplyCoverage from XP and all related functions in gpu code.

src/effects/SkArithmeticMode_gpu.h

Index: src/effects/SkArithmeticMode_gpu.h
diff --git a/src/effects/SkArithmeticMode_gpu.h b/src/effects/SkArithmeticMode_gpu.h
index 546902dd50f97b99cd10b7ea165dbff06115944c..8fb58a1796844deb74a0b191b8edda5fa22fc8ca 100644
--- a/src/effects/SkArithmeticMode_gpu.h
+++ b/src/effects/SkArithmeticMode_gpu.h
@@ -81,11 +81,6 @@ public:
         return true;
     }
 
-    bool canApplyCoverage(const GrProcOptInfo& colorPOI,
-                          const GrProcOptInfo& coveragePOI) const SK_OVERRIDE {
-        return true;
-    }
-
     bool canTweakAlphaForCoverage() const SK_OVERRIDE {
         return false;
     }