After the Call of Duty: Black Ops III - Multiplayer DLC Trial Pack goes live on May 30th, Player can opt out of the trial by following these steps:
1) In the Steam Client, select the Library dropdown and select Games.
2) In the Games section, select "Call of Duty: Black Ops III".
3) In the DLC section uncheck the checkbox of “Call of Duty: Black Ops III – Multiplayer DLC Trial Pack” to opt out of BO3 Multiplayer DLC Trial Pack.
Note: Unchecking the BO3 MP DLC Trial Pack will uninstall the DLC maps that the Player does not own.