[stubs] Remove unused StoreGlobalViaContextStub.

src/ppc/interface-descriptors-ppc.cc

Index: src/ppc/interface-descriptors-ppc.cc
diff --git a/src/ppc/interface-descriptors-ppc.cc b/src/ppc/interface-descriptors-ppc.cc
index 3ff0fde047bcc75d900134a49aa308412aeb37ee..6bffd512ff47d272e9bf4f5f6d4283a3d583c376 100644
--- a/src/ppc/interface-descriptors-ppc.cc
+++ b/src/ppc/interface-descriptors-ppc.cc
@@ -44,10 +44,6 @@ const Register StoreTransitionDescriptor::SlotRegister() { return r7; }
 const Register StoreTransitionDescriptor::VectorRegister() { return r6; }
 const Register StoreTransitionDescriptor::MapRegister() { return r8; }
 
-const Register StoreGlobalViaContextDescriptor::SlotRegister() { return r5; }
-const Register StoreGlobalViaContextDescriptor::ValueRegister() { return r3; }
-
-
 const Register StringCompareDescriptor::LeftRegister() { return r4; }
 const Register StringCompareDescriptor::RightRegister() { return r3; }