ZGC: Remove dead code in zBarrier

diff --git a/src/hotspot/share/gc/z/zBarrier.hpp b/src/hotspot/share/gc/z/zBarrier.hpp
index 7c5c1fc2acf..d57bef74f91 100644
--- a/src/hotspot/share/gc/z/zBarrier.hpp
+++ b/src/hotspot/share/gc/z/zBarrier.hpp

@@ -116,7 +114,6 @@ public:
   // Mark barrier
   static void mark_barrier_on_oop_field(volatile oop* p, bool finalizable);
   static void mark_barrier_on_oop_array(volatile oop* p, size_t length, bool finalizable);
- static void mark_barrier_on_invisible_root_oop_field(oop* p);

   // Narrow oop variants, never used.
   static oop load_barrier_on_oop_field(volatile narrowOop* p);