Simplify checks

Author: andrewor14

yarn/common/src/main/scala/org/apache/spark/deploy/yarn/ClientArguments.scala

@@ -69,12 +69,9 @@ private[spark] class ClientArguments(args: Array[String], sparkConf: SparkConf)
    * This is intended to be called only after the provided arguments have been parsed.
    */
   private def validateArgs(): Unit = {
-    Map[Boolean, String](
-      (numExecutors <= 0) -> "You must specify at least 1 executor!"
-    ).foreach { case (errorCondition, errorMessage) =>
-      if (errorCondition) {
-        throw new IllegalArgumentException(errorMessage + "\n" + getUsageMessage())
-      }
+    if (numExecutors <= 0) {
+      throw new IllegalArgumentException(
+        "You must specify at least 1 executor!\n" + getUsageMessage())
     }
   }