Remove obsolete global SubString method.

src/handles.cc

Index: src/handles.cc
diff --git a/src/handles.cc b/src/handles.cc
index 033fdab3dc6652534e76bd9d4fae19eebeb08289..6b9025dbf6306da14897b1e4656e45e7bb2aebf0 100644
--- a/src/handles.cc
+++ b/src/handles.cc
@@ -285,15 +285,6 @@ Handle<Object> LookupSingleCharacterStringFromCode(Isolate* isolate,
 }
 
 
-Handle<String> SubString(Handle<String> str,
-                         int start,
-                         int end,
-                         PretenureFlag pretenure) {
-  CALL_HEAP_FUNCTION(str->GetIsolate(),
-                     str->SubString(start, end, pretenure), String);
-}
-
-
 // Wrappers for scripts are kept alive and cached in weak global
 // handles referred from foreign objects held by the scripts as long as
 // they are used. When they are not used anymore, the garbage