FIX Remove excessive width on add new multi class dropdown
FIX Remove excessive width on add new multi class dropdown

This removes a width definition added in da2e75f

dhensby/silverstripe-gridfieldextensions,kinglozzer/silverstripe-gridfieldextensions,silverstripe-australia/silverstripe-gridfieldextensions,symbiote/silverstripe-gridfieldextensions,kinglozzer/silverstripe-gridfieldextensions,symbiote/silverstripe-gridfieldextensions,dhensby/silverstripe-gridfieldextensions,silverstripe-australia/silverstripe-gridfieldextensions