Shaving a floor joist without a planer?
If the floor framing is wide open, snap a chalkline on the side of the joist and run your circular saw on that. You could go so far as to screw a guide to the joist if you don't trust your skills, but it's a matter of finding a comfortable position and bracing against the joist with your hands. Just keep the saw table tight to the joist to keep the cut square. 

Do investigate why that joist is high, though. Is it just warped? Bad from the mill? Hung up on a beam where the framing around it has settled or sagged? You may not want to fix the problem this way if you find something underneath that should be fixed instead.