Remove trivial constructor

No functional change

Author: romainbrenguier

src/goto-symex/goto_symex_state.h

@@ -355,12 +355,7 @@ class goto_symex_statet final
     guardt guard;
     call_stackt call_stack;
     std::map<irep_idt, unsigned> function_frame;
-    unsigned atomic_section_id;
-
-    threadt():
-      atomic_section_id(0)
-    {
-    }
+    unsigned atomic_section_id = 0;
   };
 
   typedef std::vector<threadt> threadst;