[stubs] Remove unused StoreGlobalViaContextStub.

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 9e486446bc0e1358aa7518a4d0ada0ff196101c4..c697ae4b6a85f9b8f6d9e2af95e0fbe49f3e8045 100644
--- a/src/x64/interface-descriptors-x64.cc
+++ b/src/x64/interface-descriptors-x64.cc
@@ -44,10 +44,6 @@ const Register StoreTransitionDescriptor::SlotRegister() { return rdi; }
 const Register StoreTransitionDescriptor::VectorRegister() { return rbx; }
 const Register StoreTransitionDescriptor::MapRegister() { return r11; }
 
-const Register StoreGlobalViaContextDescriptor::SlotRegister() { return rbx; }
-const Register StoreGlobalViaContextDescriptor::ValueRegister() { return rax; }
-
-
 const Register StringCompareDescriptor::LeftRegister() { return rdx; }
 const Register StringCompareDescriptor::RightRegister() { return rax; }