[SPARK-3970] Remove duplicate removal of local dirs

The shutdown hook of `DiskBlockManager` would remove localDirs. So do not need to register them with `Utils.registerShutdownDeleteDir`. It causes duplicate removal of these local dirs and corresponding exceptions.
Because it tries to delete local dirs that are already removed, So it would cause exceptions as following:

    ERROR DiskBlockManager: Exception while deleting local spark dir: /tmp/spark-local-20141016160713-d38f
    java.io.IOException: Failed to list files for dir: /tmp/spark-local-20141016160713-d38f/1b
        at org.apache.spark.util.Utils$.listFilesSafely(Utils.scala:666)
        at org.apache.spark.util.Utils$.deleteRecursively(Utils.scala:680)
        .....