An international relief group that provides vaccines to poor countries says it’s phasing out some vaccines that Robert F. Kennedy Jr. believes are unsafe. The health secretary has cited Gavi’s use of the shots in blocking $600 million in U.S. funding. In a bid to get Kennedy to relent, the group on Thursday offered to speed the transition to shots that do not contain thimerosal, a mercury-containing preservative. Sen. Jeanne Shaheen (D-N.H.) has…