change update of dynamic groups to post_force location in timestep

src/update.h

@@ -35,7 +35,6 @@ class Update : protected Pointers {
   int max_eval;                  // max force evaluations for minimizer
   int restrict_output;           // 1 if output should not write dump/restart
   int setupflag;                 // set when setup() is computing forces
-  int post_integrate;            // 1 if now at post_integrate() in timestep
   int multireplica;              // 1 if min across replicas, else 0
   int dt_default;                // 1 if dt is at default value, else 0