AlbanyAn Adirondack conservation group is asking billionaire investor Warren Buffett to remove obsolete rail oil tankers now being stored indefinitely on a rail line in the Adirondacks.Adirondack Council Executive Director William Janeway wrote last week to the Nebraska investor urging that rail cars owned by subsidiaries of Buffett's Berkshire Hathaway company be removed from the line.Owned by Union Tank Car Co.