Revert "Bypass SerializationDebugger for now (SPARK-7180)"

This reverts commit 9419efe.

core/src/test/scala/org/apache/spark/util/ClosureCleanerSuite2.scala

@@ -23,7 +23,7 @@ import scala.collection.mutable
 
 import org.scalatest.{BeforeAndAfterAll, FunSuite, PrivateMethodTester}
 
-import org.apache.spark.{SparkConf, SparkContext, SparkException}
+import org.apache.spark.{SparkContext, SparkException}
 import org.apache.spark.serializer.SerializerInstance
 
 /**
@@ -38,13 +38,7 @@ class ClosureCleanerSuite2 extends FunSuite with BeforeAndAfterAll with PrivateM
   private var closureSerializer: SerializerInstance = null
 
   override def beforeAll(): Unit = {
-    val conf = new SparkConf()
-      .set("spark.master", "local")
-      .set("spark.app.name", "test")
-      // SerializationDebugger currently cannot serialize ClosureCleanerSuite2 because
-      // it has non-serializable fields but inherits a serializable class (SPARK-7180)
-      .set("spark.serializer.extraDebugInfo", "false")
-    sc = new SparkContext(conf)
+    sc = new SparkContext("local", "test")
     closureSerializer = sc.env.closureSerializer.newInstance()
   }