I had the same issue with my XL motor. I used two large flat head screw drivers. Place 'em behind the the gear on either side of the shaft and then rotate the screwdrivers together so the flat heads are hitting the inside of the gear (near the shaft).
The flat head will push the gear outwards off the motor shaft, and you don't have to worry about prying on your motor shaft and risk bending anything. Mine slide right off.
If you don't need that gear, just use a Dremel if you have one and grind it out. One of my Aveox came with a gear box and when I took the gear box out it had a 32 pitch pinion glued to the shaft. I did everything to try and get it out, but my Dremel needed some action . After your done just sand the shaft a bit with fine grit sand paper.
Yeah. If I manage to get this pinion off, I'll be at least removing a little bit of material on the inside of the pinion. I haven't had a try at prying it off yet, as I'm still disassembling and cleaning my Revo. It probably won't happen until the weekend.