There are contradicting reports as to whether or not Conor McGregor vacated his featherweight title willingly at the UFC's request or had to be stripped of it. Either way he's no longer the featherweight champ.
The reason for the vacating of the belt is the UFC wants a title fight at UFC 206. Daniel Cormier, who was supposed to defend his title, backed out of the event due to injury, The Express Tribune:
McGregor, who knocked out Eddie Alvarez this month to claim the lightweight crown and become the first fighter in the promotion’s history to hold two UFC belts simultaneously, had previously said he did not want to give up either title. He won the featherweight crown by defeating Brazilian Aldo in 13 seconds at UFC 194 last December.
In order to keep a title bout on the UFC 206 card, officials asked McGregor to relinquish his featherweight title so Max Holloway and Anthony Pettis could fight for the interim UFC featherweight championship.
McGregor's probably not going to be happy with having the title taken away, but he hasn't fought at featherweight in some time and lightweight is an easier weight for him to fight at. He also said he wasn't going to fight against until his child was born sometime early next year.