Simplify SLOT-NAME-LISTS-FROM-SLOTS and friends

Simplify SLOT-NAME-LISTS-FROM-SLOTS and friends

* Removed SYMBOL-LESSP and its helper SYMBOL-PKG-NAME

* SYMBOL-OR-CONS-LESSP compares symbol hashes instead of calling
  SYMBOL-LESSP

A FIXME comment suggested this change, giving the following rationale:

  Because of the existence of UNINTERN and RENAME-PACKAGE, the part of
  this ordering which is based on SYMBOL-PKG-NAME is not stable. This
  ordering is only used in to SLOT-NAME-LISTS-FROM-SLOTS, where it serves
  to "canonicalize the PV-TABLE's a bit and will hopefully lead to having
  fewer PV's floating around", so it sounds as though the instability
  won't actually lead to bugs, just small inefficiency. But still, it
  would be better to reimplement this function as a comparison based on
  SYMBOL-HASH:

  * stable comparison
  * smaller code (here, and in being able to discard SYMBOL-PKG-NAME)
  * faster code.