I don't think you should "take away a snack" (as in, we've always had a snack at three o'clock, but now we're not), though perhaps restricting snacking right before the meal would help (as in, "Mommy, I want some crackers." "Not right now, honey, dinner's on the stove.")
It is too much to ask a child that young to sit still and calmly for the entire course of an adult's relaxing meal. But, I don't think it's too much to ask him to sit for ten minutes and eat a reasonable portion, then go play. Not having him be full from snacking when dinner time comes will definately help, but again, it's different from "taking away a snack". Role playing to practice table manners may help. Also, tell him that cruising by and taking one bite then running away disturbs the rest of the family's meal, and it's therefore not acceptable. He may go play and come back to eat later, but in doing so he must come, sit in his chair, eat a reasonable portion, then go back to his playing without disturbing everyone. All coming and going from the table is to be done in a way that's respectful. And hold him to it.