Cleanup force.h after refactoring

  class Pair *pair;

  char *pair_style;

  typedef Pair *(*PairCreator)(LAMMPS *);

  typedef std::map<std::string,PairCreator> PairCreatorMap;

  PairCreatorMap *pair_map;

  class Bond *bond;

  char *bond_style;

  typedef Bond *(*BondCreator)(LAMMPS *);

  typedef std::map<std::string,BondCreator> BondCreatorMap;

  BondCreatorMap *bond_map;

  class Angle *angle;

  char *angle_style;

  typedef Angle *(*AngleCreator)(LAMMPS *);

  typedef std::map<std::string,AngleCreator> AngleCreatorMap;

  AngleCreatorMap *angle_map;

  class Dihedral *dihedral;

  char *dihedral_style;

  typedef Dihedral *(*DihedralCreator)(LAMMPS *);

  typedef std::map<std::string,DihedralCreator> DihedralCreatorMap;

  DihedralCreatorMap *dihedral_map;

  class Improper *improper;

  char *improper_style;

  typedef Improper *(*ImproperCreator)(LAMMPS *);

  typedef std::map<std::string,ImproperCreator> ImproperCreatorMap;

  ImproperCreatorMap *improper_map;

  class KSpace *kspace;

  char *kspace_style;

  typedef Pair *(*PairCreator)(LAMMPS *);

  typedef Bond *(*BondCreator)(LAMMPS *);

  typedef Angle *(*AngleCreator)(LAMMPS *);

  typedef Dihedral *(*DihedralCreator)(LAMMPS *);

  typedef Improper *(*ImproperCreator)(LAMMPS *);

  typedef KSpace *(*KSpaceCreator)(LAMMPS *,int,char**);

  typedef std::map<std::string,PairCreator> PairCreatorMap;

  typedef std::map<std::string,BondCreator> BondCreatorMap;

  typedef std::map<std::string,AngleCreator> AngleCreatorMap;

  typedef std::map<std::string,DihedralCreator> DihedralCreatorMap;

  typedef std::map<std::string,ImproperCreator> ImproperCreatorMap;

  typedef std::map<std::string,KSpaceCreator> KSpaceCreatorMap;

  PairCreatorMap *pair_map;

  BondCreatorMap *bond_map;

  AngleCreatorMap *angle_map;

  DihedralCreatorMap *dihedral_map;

  ImproperCreatorMap *improper_map;

  KSpaceCreatorMap *kspace_map;

                             // index [0] is not used in these arrays