remove tc7_subr_* and tc7_lsubr_*

remove tc7_subr_* and tc7_lsubr_*

* libguile/tags.h: Remove tc7 #defines for subrs, replacing them with
  placeholders. These were public, but hopfully unused. I don't see how
  to usefully deprecate them.

* libguile/array-map.c (scm_array_map_x): Remove special cases for
  certain subr types. This might make things slower for the moment,
  otoh, native compilation should moot that question.

* libguile/eval.i.c:
* libguile/eval.c: Remove subr-handling cases. To regain this speed and
  more won't have to wait for native compilation, though -- this change
  smooths the way for subr dispatch in the VM.

* libguile/gsubr.c (scm_i_gsubr_apply): Fix a bug in which we didn't
  detect too-many-arguments. This would only show up when using ceval,
  as only ceval called this function.

* test-suite/tests/ramap.test ("array-map!"): Change the expected
  exception if passed a procedure of the wrong arity. It now gives
  wrong-num-args.
  more won't have to wait for native compilation, though -- this change
  smooths the way for subr dispatch in the VM.

* libguile/goops.c (scm_class_of): Remove subr cases. No speed
  implication.

* libguile/objects.c (scm_valid_object_procedure_p): Remove this public
  but undocumented, and useless, function. I do not think this will
  affect anyone at all.
  (scm_set_object_procedure_x): Replace a call to
  scm_valid_object_procedure_p with scm_procedure_p, and actually wrap
  with a scm_is_true.

* module/oop/goops.scm (initialize-object-procedure): Don't call
  valid-object-procedure?.