How to remove imported contacts?

We purchased an iMac. I also own a macbook and iPhone (prior to this). All three devices synced. My husband used the iMac and imported his Linkedin contacts but was not trying to put them into the iMac contacts (not sure exactly what he was doing, but oh well). Now all 500 of those contacts show up on all my devices. I want them off. The Linkedin import shows up as a group in the contacts and also shows up under smart groups as the last import. Is there a way I can remove them from the total list of contacts without having to do it one by one?