Obsolete comment above _bt_doinsert()

The comments above _bt_doinsert() say at one point:

 *        This routine is called by the public interface routines, btbuild
 *        and btinsert.  By here, itup is filled in, including the TID, in
 *        contrast with _bt_lockinsert() where the heap tuple is not yet
 *        inserted.

This is obsolete; since commit 89bda95d, only the insert public
interface routine calls _bt_doinsert().

--
Peter Geoghegan