[cleanup] Drop unused scratch register from {load,store}_calling_convention

src/ic/access-compiler.h

Index: src/ic/access-compiler.h
diff --git a/src/ic/access-compiler.h b/src/ic/access-compiler.h
index 50c2cc7303a38e63ec4f1f252d05540063aaa14a..ecc5c08a599931d16458812bd8c40e40b5b4e1c1 100644
--- a/src/ic/access-compiler.h
+++ b/src/ic/access-compiler.h
@@ -58,7 +58,6 @@ class PropertyAccessCompiler BASE_EMBEDDED {
   Register vector() const;
   Register scratch1() const { return registers_[2]; }
   Register scratch2() const { return registers_[3]; }
-  Register scratch3() const { return registers_[4]; }
 
   static Register* GetCallingConvention(Code::Kind);
   static Register* load_calling_convention();