Just cut as close to the wall as you can, preferable right up to the wall. Read your installation questions to see how far from the 'end' of the planks you must nail, and that will tell you how close to the wall you need to get. You can use a reciprocating saw, very carefully, to a less-than-hitting-the-joists depth, then hand chissel the rest out. You may not need to do this if you nail your planks, say, 1" from the end of the plank. You technically need support where you walk. And that's no where near 2" from the wall, well, at least all the time. You should nail your subfloor right into the floor joists. Chalk or pencil-out the sheets so you know where the joists are once you lay the sheets down. Make sure the ends of the sheets run to the middle of the joist. Your flooring install instructions will guide you on this step. Be SURE to read it first! The major issue here is that you don't cut into your joists more than, well, 1/4". That's why when doing this type of job, it's best to set the depth of your saw to a depth just a little shy of the actual thickness of the existing subfloor.
If you have any further concerns, contact the Retailer or the Mfgr for guidance. My best to ya and hope this helps.
PS: Cut out what you can of the subfloor with a power saw first, then remove what you need/want along the edges afterwords. To know how thick your subfloor is, find a heating duct on the floor, pull off the cover, and look at the edge. You may need a mirror or you may be able to just measure it.