Eliminate redundant descriptor ElementTransitionAndStoreDescriptor.

src/x64/interface-descriptors-x64.cc

Index: src/x64/interface-descriptors-x64.cc
diff --git a/src/x64/interface-descriptors-x64.cc b/src/x64/interface-descriptors-x64.cc
index 40bff24f5128e246e361eac4c4fee96948b37c00..9b32ffbc3321734204a4ab1213d0c2878de2ad32 100644
--- a/src/x64/interface-descriptors-x64.cc
+++ b/src/x64/interface-descriptors-x64.cc
@@ -47,11 +47,6 @@ const Register StoreGlobalViaContextDescriptor::NameRegister() { return rcx; }
 const Register StoreGlobalViaContextDescriptor::ValueRegister() { return rax; }
 
 
-const Register ElementTransitionAndStoreDescriptor::MapRegister() {
-  return rbx;
-}
-
-
 const Register InstanceofDescriptor::left() { return rax; }
 const Register InstanceofDescriptor::right() { return rdx; }