Remove obsolete nbtree "get root" comment.
Remove a very old Berkeley era comment that doesn't seem to have
anything to do with the current locking considerations within
_bt_getroot().
Discussion:
@@ -266,9 +266,7 @@ _bt_update_meta_cleanup_info(Relation rel, TransactionId oldestBtpoXact,
*
* Since the root page can move around the btree file, we have to read
* its location from the metadata page, and then read the root page
- * itself. If no root page exists yet, we have to create one. The
- * standard class of race conditions exists here; I think I covered
- * them all in the intricate dance of lock requests below.
+ * itself. If no root page exists yet, we have to create one.
*
* The access type parameter (BT_READ or BT_WRITE) controls whether
* a new root page will be created or not. If access = BT_READ,
