1.0.29.22: smattering of DOCUMENTATION cleanups

* Delete stale function documentation: STEP-CONDITION-SOURCE-PATH and
  STEP-CONDITION-PATHNAME no longer exist.

* Move RANDOM-DOCUMENTATION to SB-KERNEL, use it in FDOCUMENTATION.

* Replace bare INFO calls from DOCUMENTATION methods with calls to
  FDOCUMENTATION, as per FIXME.

* Make FDOCUMENTATION work on '(SETF FOO) names, and delete the
  DEFKNOWNs for it.