Removed redundant TaskSetManager.error() function.

This function was leftover from a while ago, and now just
passes all calls through to the abort() function, so this
commit deletes it.

core/src/main/scala/org/apache/spark/scheduler/TaskSchedulerImpl.scala

@@ -328,7 +328,7 @@ private[spark] class TaskSchedulerImpl(
         // Have each task set throw a SparkException with the error
         for ((taskSetId, manager) <- activeTaskSets) {
           try {
-            manager.error(message)
+            manager.abort(message)
           } catch {
             case e: Exception => logError("Exception in error callback", e)
           }

core/src/main/scala/org/apache/spark/scheduler/TaskSetManager.scala

@@ -548,11 +548,6 @@ private[spark] class TaskSetManager(
     }
   }
 
-  def error(message: String) {
-    // Save the error message
-    abort("Error: " + message)
-  }
-
   def abort(message: String) {
     // TODO: Kill running tasks if we were not terminated due to a Mesos error
     sched.dagScheduler.taskSetFailed(taskSet, message)