Are you referring to the part of the screen above the message but below where it says "Group"? If you don't want to see how's in the group, then name that group conversation. Tap "Details" and then swipe downward; at the top of the screen you'll see "Group Name: Enter a Group Name." Name it what ever you like (knowing that everyone in the group will see the same group name). From then on you won't see the individual people in the group listed on the message screen; you'll need to tap on "Details" to see who is in the group.
Note also that the group name can be changed or removed at a later time.