Just got a Surefire M-900 that I'm mounting on a rail underneath my M4 handguards. Problem is that the front sling attatchment hangs down far enough that it taps the very top of  light.

I'm getting a side sling adapter next week, so I don't think I need it. So should I just remove it? And if so, how do I go about it? Just punch that pin out from the side?

The best way that I have found to remove the rivet holding the front sling swivel on is to use a rotary tool with one of the cutting wheels. Just grind off the end that is the thinnest.

I've used a punch on 2 of my Bushmaster uppers.  One good thwack and 2 decent taps and it's out.

Put down the Dremel and step away before anybody gets hurt!

The rivet is made of a very soft metal.  The end with the hole in it (where the metal was bent into place when the rivet was installed) can be driven out by doing like Vinnie said and use a very small punch to drive it out.  I've had the best results using a pair of pliers to squeeze the open end so that there is less metal holding the rivet in place then using a nail punch to drive it out.