Remove stage builder and use ID's in unwindOrder (#2381)

cmd/hack/hack.go

cmd/integration/commands/snapshot_check.go

cmd/integration/commands/stages.go

cmd/integration/commands/state_stages.go

eth/backend.go

eth/fetcher/tx_fetcher.go

eth/integrity/trie.go

eth/stagedsync/default_stages.go

eth/stagedsync/stage.go

eth/stagedsync/stage_bodies_snapshot.go

eth/stagedsync/stage_execute.go

eth/stagedsync/stage_execute_test.go

eth/stagedsync/stage_hashstate.go

eth/stagedsync/stage_headers_snapshot.go

eth/stagedsync/stage_interhashes.go

eth/stagedsync/stage_senders.go

eth/stagedsync/stage_senders_test.go

eth/stagedsync/stagebuilder.go

eth/stagedsync/stagedsync.go

eth/stagedsync/state.go