[FAB-11863] Remove redudant return value in GetChain

common/deliver/deliver.go

common/deliver/deliver_test.go

common/deliver/mock/chain_manager.go

core/peer/deliverevents_test.go

core/peer/peer.go

core/peer/peer_test.go

orderer/common/multichannel/registrar.go

orderer/common/multichannel/registrar_test.go

orderer/common/server/server.go

orderer/consensus/etcdraft/consenter.go

orderer/consensus/etcdraft/consenter_test.go

orderer/consensus/etcdraft/mocks/chain_getter.go