Remove MVRA from VM frames

Remove MVRA from VM frames

* libguile/_scm.h (SCM_OBJCODE_MINOR_VERSION): Bump for frame layout
  change.

* libguile/frames.c: Update some static checks.
  (scm_frame_num_locals, scm_frame_local_ref, scm_frame_local_set_x):
  Update to not skip over uninitialized frames, as that's not a thing
  any more.

* libguile/frames.h: Update to remove MVRA.  Woo!

* libguile/vm-engine.c (ALLOC_FRAME, RETURN_ONE_VALUE):
  (rtl_vm_engine): Update for 3 words per frame instead of 4.

* libguile/vm.c (vm_return_to_continuation): Likewise.

* module/language/cps/slot-allocation.scm (allocate-slots): 3 words per
  frame, not 4.

* module/system/vm/assembler.scm (*bytecode-minor-version*): Bump.  Also
  remove a couple of tc7's that aren't around any more.