btvacuumpage useless "orig_blkno"

I just noticed that btvacuumpage has two BlockNumber parameters -- blkno
and orig_blkno.  The only caller passes them as the same value; the
header comments state that blkno would be different when recursing, but
actually the function implements recursion internally by way of a cute
"goto" trick.  So it seems to me that the orig_blkno parameter is
useless -- we could just remove it.

Unless I'm completely missing something?

-- 
Álvaro Herrera <alvherre@alvh.no-ip.org>