Since the move to BDW-GC this option has not been useful.

* libguile/__scm.h (SCM_DEBUG_CELL_ACCESSES): Remove default
  definition.
* libguile/gc.h: Add comment about cells.
  (SCM_VALIDATE_CELL): Remove.  I did a search on the internet and I
  found no external users.
  (SCM_CELL_WORD, SCM_CELL_OBJECT, SCM_SET_CELL_WORD)
  (SCM_SET_CELL_OBJECT, SCM_CELL_OBJECT_LOC): Remove SCM_VALIDATE_CELL
  uses.
* libguile/gc.c (scm_debug_cell_accesses_p)
  (scm_expensive_debug_cell_accesses_p)
  (scm_debug_cells_gc_interval, scm_i_expensive_validation_check)
  (scm_assert_cell_valid): Remove bindings only available when
  SCM_DEBUG_CELL_ACCESSES was 1.
* libguile/list.c (scm_list_n): Remove SCM_VALIDATE_CELL usage.