2976 remove useless offsetof() macros

*** 670,682 ****
  #define fr_tif          fr_tifs[0]
  #define fr_rif          fr_tifs[1]
  
  #define FR_NOLOGTAG     0
  
- #ifndef offsetof
- #define offsetof(t,m)   (size_t)((&((t *)0)->m))
- #endif
  #define FR_CMPSIZ       (sizeof(struct frentry) - \
                           offsetof(struct frentry, fr_func))
  
  /*
   * fr_type
--- 670,679 ----