Remove unimplemented declaration

Author: romainbrenguier

src/goto-symex/goto_symex_state.h

@@ -363,9 +363,6 @@ class goto_symex_statet final
   bool l2_thread_read_encoding(ssa_exprt &expr, const namespacet &ns);
   bool l2_thread_write_encoding(const ssa_exprt &expr, const namespacet &ns);
 
-  void populate_dirty_for_function(
-    const irep_idt &id, const goto_functiont &);
-
   void switch_to_thread(unsigned t);
   bool record_events;
   incremental_dirtyt dirty;