Allow the static allocation of all types of subrs.

Allow the static allocation of all types of subrs.

This is a follow-up to 46f9baf49a8ea4461e8494c75a88b87d0f5c5195 ("Allow
the static initialization of subrs.") and
e20d7001c3f7150400169fecb0bf0eefdf122fe2 ("Remove "compiled closures"
("cclos") in favor of a simpler mechanism.").

* libguile/procs.h (SCM_SUBR_ARITY_TO_TYPE): Return the appropriate type
  for gsubrs instead of returning -1.

* libguile/Makefile.am (snarf-gsubr.h): Remove target.
  (BUILT_SOURCES, nodist_modinclude_HEADERS, MOSTLYCLEANFILES): Remove
  `snarf-gsubr.h'.

* libguile/snarf.h (SCM_DEFINE)[SCM_SUPPORT_STATIC_ALLOCATION]: Don't
  include "libguile/snarf-gsubr.h".
  (SCM_DEFINE_SUBR_reqX_optY_rstZ): Remove.