Snapshots: retire blocks by default (#3707)

cmd/downloader/readme.md

cmd/integration/commands/flags.go

cmd/integration/commands/stages.go

cmd/rpcdaemon/cli/config.go

cmd/state/commands/erigon2.go

cmd/utils/flags.go

core/rawdb/accessors_chain.go

eth/backend.go

eth/ethconfig/config.go

eth/stagedsync/stage_headers.go

eth/stagedsync/stage_senders.go

eth/stagedsync/stage_senders_test.go

turbo/app/snapshots.go

turbo/cli/default_flags.go

turbo/snapshotsync/block_reader.go

turbo/snapshotsync/block_snapshots.go

turbo/snapshotsync/block_snapshots_test.go

turbo/snapshotsync/snapshotsynccli/flags.go

turbo/stages/mock_sentry.go

turbo/stages/stageloop.go