[stubs] Remove unused StoreGlobalViaContextStub.

src/s390/interface-descriptors-s390.cc

Index: src/s390/interface-descriptors-s390.cc
diff --git a/src/s390/interface-descriptors-s390.cc b/src/s390/interface-descriptors-s390.cc
index ca40a0c9f1a9627afeedead1d7bc8190f1714196..3e0de13ad4e6ed70584d1f85b7931d9c12f63d64 100644
--- a/src/s390/interface-descriptors-s390.cc
+++ b/src/s390/interface-descriptors-s390.cc
@@ -42,9 +42,6 @@ const Register StoreTransitionDescriptor::SlotRegister() { return r6; }
 const Register StoreTransitionDescriptor::VectorRegister() { return r5; }
 const Register StoreTransitionDescriptor::MapRegister() { return r7; }
 
-const Register StoreGlobalViaContextDescriptor::SlotRegister() { return r4; }
-const Register StoreGlobalViaContextDescriptor::ValueRegister() { return r2; }
-
 const Register StringCompareDescriptor::LeftRegister() { return r3; }
 const Register StringCompareDescriptor::RightRegister() { return r2; }