fix(consensus): count hooray only after successful final commit

[mur-me]

Remove the premature UpdateLeaderMetrics call from onPrepare.

The metric is already updated in _finalCommit after the leader successfully commits the block and logs HOORAY!!!!!!! CONSENSUS REACHED!!!!!!!

This prevents hooray and num_commits from being inflated for every received PREPARE message.

Test

Previously it was showing a huge increase of the metrics, because it was counting prepare:

sum by (instance, job) (
  increase(
    hmy_consensus_bingo{
      consensus=~"hooray",
      instance=~"$instance.*",
      job=~"$shard"
    }[1m]
  )
) > 0

Tested fix on the shard 1 devnet, you can see 60 hooray + bingos vs 600 prepare in the shard 0: