Not a lot of text needed for this suggestion, title almost says it all. There's a bunch of older clan skins that I haven't seen getting used for the past 14 months I've played.
The clan skins I haven't seen in the past 6 months of playing on both pvp servers and official servers are:
[IDTI] , [MMFK] , [187K] , [UNIT] (the MLG ones) , [VG] , [NP2] , [RWL7] , last but not least, a black and red skin, which when you apply it, it says "å~>>AGå>>" which seems bugged out.
Removing all of the inactive skins would make the game optimized, aswell as it COULD open up opportunities to have clan skins for more active clans, but with very strict rules, and in case the rules are not followed properly, the skin could get removed.