Remove leading NIL from slot name lists

A FIXME comment said:

  NIL at the head of the list is a remnant from old purged code, that
  hasn't been quite cleaned up yet.

Changed producers of such lists:

* SLOT-NAME-LISTS-FROM-SLOTS
* MAKE-STD-{WRITER,READER,BOUNDP}-METHOD-FUNCTION

Changed consumers:

* INTERN-PV-TABLE
* COMPUTE-PV

src/pcl/slots-boot.lisp

@@ -444,7 +444,7 @@
                              .pv. instance-slots 0
                              (slot-value instance slot-name))))))))
        (setf (getf (getf initargs 'plist) :slot-name-lists)
-             (list (list nil slot-name)))
+             (list (list slot-name)))
        initargs))
     ((:custom :accessor)
      (let* ((initargs (copy-tree
@@ -454,7 +454,7 @@
                                         (instance) nil)
                             (instance-read-custom .pv. 0 instance)))))))
        (setf (getf (getf initargs 'plist) :slot-name-lists)
-             (list (list nil slot-name)))
+             (list (list slot-name)))
        initargs))))
 
 (defun make-std-writer-method-function (class-or-name slot-name)
@@ -479,7 +479,7 @@
                                   .pv. instance-slots 0 nv
                                   (setf (slot-value instance slot-name) .good-new-value.)))))))))
          (setf (getf (getf initargs 'plist) :slot-name-lists)
-               (list nil (list nil slot-name)))
+               (list nil (list slot-name)))
          initargs))
      ((:custom :accessor)
       (let ((initargs (copy-tree
@@ -489,7 +489,7 @@
                                         (instance) nil)
                             (instance-write-custom .pv. 0 instance nv)))))))
         (setf (getf (getf initargs 'plist) :slot-name-lists)
-              (list nil (list nil slot-name)))
+              (list nil (list slot-name)))
         initargs)))))
 
 (defun make-std-boundp-method-function (class-or-name slot-name)
@@ -504,7 +504,7 @@
                             .pv. instance-slots 0
                             (slot-boundp instance slot-name))))))))
        (setf (getf (getf initargs 'plist) :slot-name-lists)
-             (list (list nil slot-name)))
+             (list (list slot-name)))
        initargs))
     ((:custom :accessor)
      (let ((initargs (copy-tree
@@ -514,7 +514,7 @@
                                        (instance) nil)
                            (instance-boundp-custom .pv. 0 instance)))))))
        (setf (getf (getf initargs 'plist) :slot-name-lists)
-             (list (list nil slot-name)))
+             (list (list slot-name)))
        initargs))))
 
 ;;;; FINDING SLOT DEFINITIONS

src/pcl/vector.lisp

@@ -63,20 +63,13 @@
 
 (defun intern-pv-table (&key slot-name-lists)
   (flet ((intern-slot-names (slot-names)
-           ;; FIXME: NIL at the head of the list is a remnant from
-           ;; old purged code, that hasn't been quite cleaned up yet.
-           ;; ...but as long as we assume it is there, we may as well
-           ;; assert it.
-           (aver (not (car slot-names)))
            (or (gethash slot-names *slot-name-lists*)
                (setf (gethash slot-names *slot-name-lists*) slot-names)))
          (%intern-pv-table (snl)
            (or (gethash snl *pv-tables*)
                (setf (gethash snl *pv-tables*)
                      (make-pv-table :slot-name-lists snl
-                                    :pv-size (* 2 (reduce #'+ snl
-                                                          :key (lambda (slots)
-                                                                 (length (cdr slots))))))))))
+                                    :pv-size (* 2 (reduce #'+ snl :key #'length)))))))
     (sb-thread:with-mutex (*pv-lock*)
       (%intern-pv-table (mapcar #'intern-slot-names slot-name-lists)))))
 
@@ -105,7 +98,7 @@
         (let* ((wrapper (pop wrappers))
                (std-p (layout-for-std-class-p wrapper))
                (class (wrapper-class* wrapper)))
-          (dolist (slot-name (cdr slot-names))
+          (dolist (slot-name slot-names)
             (let ((cell
                     (or (find-slot-cell wrapper slot-name)
                         (cons nil (slot-missing-info class slot-name)))))
@@ -533,7 +526,7 @@
 (defun slot-name-lists-from-slots (slots)
   (mapcar (lambda (parameter-entry)
             (when (cdr parameter-entry)
-              (cons nil (mapcar #'car (cdr parameter-entry)))))
+              (mapcar #'car (cdr parameter-entry))))
           (mutate-slots slots)))
 
 (defun mutate-slots (slots)