Simplify stagedsync.Prepare (#2317)

cmd/integration/commands/stages.go

cmd/integration/commands/state_stages.go

cmd/rpcdaemon/commands/send_transaction_test.go

cmd/rpcdaemon/commands/txpool_api_test.go

cmd/snapshots/debug/debug_test.go

eth/backend.go

eth/ethconfig/config.go

eth/filters/filter_system_test.go

eth/filters/filter_test.go

eth/stagedsync/default_stages.go

eth/stagedsync/stage_bodies_snapshot.go

eth/stagedsync/stage_finish.go

eth/stagedsync/stage_headers_snapshot.go

eth/stagedsync/stage_state_snapshot.go

eth/stagedsync/stagebuilder.go

eth/stagedsync/stagedsync.go

turbo/cli/flags.go

turbo/stages/mock_sentry.go

turbo/stages/sentry_mock_test.go

turbo/stages/stageloop.go