Remove leftover mentions of XLOG_HEAP2_FREEZE_PAGE records

f83d709760 merged the separate XLOG_HEAP2_FREEZE_PAGE records into a
new combined prune, freeze, and vacuum record with opcode
XLOG_HEAP2_PRUNE_VACUUM_SCAN. Remove the last few references to
XLOG_HEAP2_FREEZE_PAGE records which were accidentally left behind.

Reported-by: Tomas Vondra
Reviewed-by: Robert Haas
Discussion: https://postgr.es/m/CA%2BTgmoY1tYff-1CEn8kYt5FsOrynTbtr%3DUZw%3D7mTC1Hv1HpeBQ%40mail.gmail.com

src/backend/access/heap/pruneheap.c

@@ -1906,7 +1906,7 @@ heap_log_freeze_eq(xlhp_freeze_plan *plan, HeapTupleFreeze *frz)
 }
 
 /*
- * Comparator used to deduplicate XLOG_HEAP2_FREEZE_PAGE freeze plans
+ * Comparator used to deduplicate the freeze plans used in WAL records.
  */
 static int
 heap_log_freeze_cmp(const void *arg1, const void *arg2)
@@ -1966,7 +1966,7 @@ heap_log_freeze_new_plan(xlhp_freeze_plan *plan, HeapTupleFreeze *frz)
 
 /*
  * Deduplicate tuple-based freeze plans so that each distinct set of
- * processing steps is only stored once in XLOG_HEAP2_FREEZE_PAGE records.
+ * processing steps is only stored once in the WAL record.
  * Called during original execution of freezing (for logged relations).
  *
  * Return value is number of plans set in *plans_out for caller.  Also writes