Remove deprecated lag metric

For next release

modules/common/src/main/mon.scala

@@ -159,8 +159,6 @@ object mon {
       object trace {
         def create = makeTrace("round.move.trace")
       }
-      val networkLag = rec("round.move.network_lag") // Deprecated.
-
       object lag {
         val avgReported = rec("round.move.lag.avg_reported")
         val estimateError = rec("round.move.lag.estimate_error")

modules/round/src/main/Round.scala

@@ -244,7 +244,6 @@ private[round] final class Round(
         pov.player.userId.foreach { UserLagCache.put(_, lag) }
         if (pov.game.playedTurns < 12) {
           import lila.mon.round.move.{ lag => lRec }
-          lila.mon.round.move.networkLag(lag.millis) // Deprecated.
           lRec.avgReported(lag.centis)
           lt.history match {
             case h: DecayingStats => lRec.compDeviation(h.deviation.toInt)