Remove typedef used only once

Author: romainbrenguier

src/goto-symex/goto_symex_state.h

@@ -358,8 +358,7 @@ class goto_symex_statet final
     unsigned atomic_section_id = 0;
   };
 
-  typedef std::vector<threadt> threadst;
-  threadst threads;
+  std::vector<threadt> threads;
 
   bool l2_thread_read_encoding(ssa_exprt &expr, const namespacet &ns);
   bool l2_thread_write_encoding(const ssa_exprt &expr, const namespacet &ns);