remove unused monitoring

modules/common/src/main/WorkQueue.scala

@@ -43,7 +43,6 @@ final class WorkQueue(buffer: Int, name: String, parallelism: Int = 1)(
       case (task, promise) =>
         task() tap promise.completeWith recover {
           case e: Exception =>
-            lila.mon.workQueue.taskFail(name).increment()
             lila.log(s"WorkQueue:$name").warn("task failed", e)
         }
     }

modules/common/src/main/mon.scala

@@ -545,7 +545,6 @@ object mon {
           "result" -> result
         )
       )
-    def taskFail(name: String) = counter("workQueue.taskFail").withTag("name", name)
   }
 
   def chronoSync[A] = lila.common.Chronometer.syncMon[A] _