Remove unneeded VM SMOB mark/free procedures.

Remove unneeded VM SMOB mark/free procedures.

* libguile/vm.c (vm_mark_stack, vm_cont_mark, vm_cont_free, vm_mark,
  vm_free): Remove.
  (scm_bootstrap_vm): Remove corresponding `scm_set_smob_mark ()' and
  `scm_set_smob_free ()' calls.

* libguile/frames.c (vm_frame_mark, vm_frame_free): Remove.
  (scm_bootstrap_frames): Remove `scm_set_smob_mark ()' and
  `scm_set_smob_free ()' calls.

* libguile/objcodes.c (objcode_mark): Remove.
  (scm_bootstrap_objcodes): Remove call to `scm_set_smob_mark ()'.

* libguile/programs.c (program_mark): Remove.
  (scm_bootstrap_programs): Remove call to `scm_set_smob_mark ()'.