Revert "[MINOR] [CORE] Warn users who try to cache RDDs with dynamic allocation on."

This reverts commit d208047.

Author: pwendell

core/src/main/scala/org/apache/spark/SparkContext.scala

@@ -1150,11 +1150,6 @@ class SparkContext(config: SparkConf) extends Logging with ExecutorAllocationCli
    * Register an RDD to be persisted in memory and/or disk storage
    */
   private[spark] def persistRDD(rdd: RDD[_]) {
-    _executorAllocationManager.foreach { _ =>
-      logWarning(
-        s"Dynamic allocation currently does not support cached RDDs. Cached data for RDD " +
-        s"${rdd.id} will be lost when executors are removed.")
-    }
     persistentRdds(rdd.id) = rdd
   }