[stubs] Remove unused StoreGlobalViaContextStub.

src/mips64/interface-descriptors-mips64.cc

Index: src/mips64/interface-descriptors-mips64.cc
diff --git a/src/mips64/interface-descriptors-mips64.cc b/src/mips64/interface-descriptors-mips64.cc
index e5b9c2e7bd07957b512dc53e942388a239a6aab8..20f5d77f247c2cb5c3fac1be205d987d011f125c 100644
--- a/src/mips64/interface-descriptors-mips64.cc
+++ b/src/mips64/interface-descriptors-mips64.cc
@@ -44,10 +44,6 @@ const Register StoreTransitionDescriptor::SlotRegister() { return a4; }
 const Register StoreTransitionDescriptor::VectorRegister() { return a3; }
 const Register StoreTransitionDescriptor::MapRegister() { return a5; }
 
-const Register StoreGlobalViaContextDescriptor::SlotRegister() { return a2; }
-const Register StoreGlobalViaContextDescriptor::ValueRegister() { return a0; }
-
-
 const Register StringCompareDescriptor::LeftRegister() { return a1; }
 const Register StringCompareDescriptor::RightRegister() { return a0; }