Revise block time metrics

[Wondertan]

• Keep the delivery based block time as is in p2p subscriber metrics
• Remove "hdr_sync_actual_blockTime_ts_hist" metric as useless
• Add two more metrics to syncer
  • header.Time - header-1.Time - "header time as committed in the chain"
  • time.Now - header.Time - "delay between actual header time and delivery"
    • could actually be part of p2p metrics