In order to circumvent the number of duplicate foo:count metrics increasing
without bounds, it's time for a rearrangement.

The following are all deprecated, and replaced with synapse_util_metrics_block_count:
  synapse_util_metrics_block_timer:count
  synapse_util_metrics_block_ru_utime:count
  synapse_util_metrics_block_ru_stime:count
  synapse_util_metrics_block_db_txn_count:count
  synapse_util_metrics_block_db_txn_duration:count

The following are all deprecated, and replaced with synapse_http_server_response_count:
   synapse_http_server_requests
   synapse_http_server_response_time:count
   synapse_http_server_response_ru_utime:count
   synapse_http_server_response_ru_stime:count
   synapse_http_server_response_db_txn_count:count
   synapse_http_server_response_db_txn_duration:count

The following are renamed (the old metrics are kept for now, but deprecated):

  synapse_util_metrics_block_timer:total ->
     synapse_util_metrics_block_time_seconds

  synapse_util_metrics_block_ru_utime:total ->
     synapse_util_metrics_block_ru_utime_seconds

  synapse_util_metrics_block_ru_stime:total ->
     synapse_util_metrics_block_ru_stime_seconds

  synapse_util_metrics_block_db_txn_count:total ->
     synapse_util_metrics_block_db_txn_count

  synapse_util_metrics_block_db_txn_duration:total ->
     synapse_util_metrics_block_db_txn_duration_seconds

  synapse_http_server_response_time:total ->
     synapse_http_server_response_time_seconds

  synapse_http_server_response_ru_utime:total ->
     synapse_http_server_response_ru_utime_seconds

  synapse_http_server_response_ru_stime:total ->
     synapse_http_server_response_ru_stime_seconds

   synapse_http_server_response_db_txn_count:total ->
      synapse_http_server_response_db_txn_count

   synapse_http_server_response_db_txn_duration:total
      synapse_http_server_response_db_txn_duration_seconds