remove "discouraged" infrastructure

remove "discouraged" infrastructure

* libguile/discouraged.h: Remove.

* libguile/deprecated.c (scm_internal_select, scm_thread_sleep)
  (scm_thread_usleep): Deprecate formerly discouraged names.

* libguile/eq.h (SCM_EQ_P):
* libguile/pairs.h (SCM_NULLP, SCM_NNULLP, SCM_CONSP, SCM_NCONSP):
* libguile/boolean.h (SCM_FALSEP, SCM_NFALSEP, SCM_BOOLP, SCM_BOOL):
  (SCM_NEGATE_BOOL, SCM_BOOL_NOT): Undiscourage these names, because I'm
  not sure deprecating them will do any good.

* libguile.h:
* libguile/gen-scmconfig.c:
* libguile/numbers.c:
* libguile/init.c:
* libguile/Makefile.am:
* configure.ac: Remove bits that referenced discouraged.h, and dealt
  with the "discouraging" system.