- Removing two copies of the drop_routine.
  Adding a shared and much simplified version.

- Removing LEX metods:
      bool stmt_drop_function(const DDL_options_st &options,
                              const Lex_ident_sys_st &db,
                              const Lex_ident_sys_st &name);

      bool stmt_drop_function(const DDL_options_st &options,
                              const Lex_ident_sys_st &name);

      bool stmt_drop_procedure(const DDL_options_st &options,
                               sp_name *name);

  The code inside the methods was very similar.
  Adding one method instead:

      bool stmt_drop_routine(const Sp_handler *sph,
                          const DDL_options_st &options,
                          const Lex_ident_sys_st &db,
                          const Lex_ident_sys_st &name);

- Adding a new virtual method Sp_handler:sqlcom_drop().
  It helped to unify the code inside the new stmt_drop_routine().