I kept in touch with the few that were precious to me - those friends whom I am actually close with or can see myself becoming close with. I still have like 6 close friends whom I keep in contact with. However the rest, I had just not contacted in an attempt to move away from those friendships cus I only ever invited them to things cus we're in a group and it's simple courtesy to invite them as well. However I do make an effort to keep in touch with them as well if they show a desire to stay friends, as two of them have, so those two I've actively sometimes said let's meet up.
Just be sure not to lose touch with those who really see you as a friend. Those people, even if you're not as close to them as they are to you, keep in touch with them as a little courtesy and just to value the fact that you have a friendship in them, even if they're closer to you than vice versa. And if those whom you wanted to lose touch with actively seeks you out, then they show a desire to stay friends, so it's worth keeping.