Suppress jmh file report

Otherwise, it will write report to a file `out`, which conflicts
with the `out` folder in the lampepfl/bench project.

bench-run/src/main/scala/dotty/tools/benchmarks/Main.scala

@@ -42,15 +42,14 @@ object Bench {
       .measurementTime(TimeValue.milliseconds(500))
       .forks(forks)
       .include(args1(0))
-      .resultFormat(ResultFormatType.CSV)
 
     if (args1.length > 1 && args1(1) != "--") {
       for ((param, values) <- paramsFromFile("inputs/" ++ args1(1)))
         builder = builder.param(param, values: _*)
     }
 
     if (args1.length > 2) {
-      builder = builder.result(args1(2))
+      builder = builder.resultFormat(ResultFormatType.CSV).result(args1(2))
     }
 
     val runner = new Runner(builder.build)