[es6] Reintroduce the instanceof operator in the backends.

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 469ff4778b8da74cd23cc68ed2bbda3ccd07505c..e1e7f9cb4669ed573e6be226cfad7c9c8df2af58 100644
--- a/src/x64/interface-descriptors-x64.cc
+++ b/src/x64/interface-descriptors-x64.cc
@@ -46,10 +46,6 @@ const Register StoreGlobalViaContextDescriptor::SlotRegister() { return rbx; }
 const Register StoreGlobalViaContextDescriptor::ValueRegister() { return rax; }
 
 
-const Register InstanceOfDescriptor::LeftRegister() { return rdx; }
-const Register InstanceOfDescriptor::RightRegister() { return rax; }
-
-
 const Register StringCompareDescriptor::LeftRegister() { return rdx; }
 const Register StringCompareDescriptor::RightRegister() { return rax; }