nbtree: Remove obsolete _bt_pgaddtup() comments.
Remove comments that are a throw back to a time when nbtree cared about
write-ordering dependencies.  The comments are similar to those removed
by commit among others.
@@ -2531,11 +2531,6 @@ _bt_newroot(Relation rel, Buffer lbuf, Buffer rbuf)
/*
* _bt_pgaddtup() -- add a data item to a particular page during split.
*
- * This routine adds the tuple to the page as requested. It does
- * not affect pin/lock status, but you'd better have a write lock
- * and pin on the target buffer! Don't forget to write and release
- * the buffer afterwards, either.
- *
* The difference between this routine and a bare PageAddItem call is
* that this code knows that the leftmost data item on an internal
* btree page has a key that must be treated as minus infinity.
