8224214: [AIX] Remove support for legacy xlc compiler

Reviewed-by: erikj, kbarrett, mdoerr, dholmes

src/hotspot/share/gc/shared/ptrQueue.hpp

@@ -211,7 +211,6 @@ class BufferNode {
 
   static BufferNode* volatile* next_ptr(BufferNode& bn) { return &bn._next; }
 
-AIX_ONLY(public:)               // xlC 12 on AIX doesn't implement C++ DR45.
   // Allocate a new BufferNode with the "buffer" having size elements.
   static BufferNode* allocate(size_t size);