Revert "Improvement on future: add stack trace to future failures."

lib/core/future.dart

Index: lib/core/future.dart
diff --git a/lib/core/future.dart b/lib/core/future.dart
index 902432a64b90aa0a49be44957923cc0976fc79ea..99af2415180efcd019af18bce4ad6a7800ef087b 100644
--- a/lib/core/future.dart
+++ b/lib/core/future.dart
@@ -193,28 +193,6 @@ class FutureAlreadyCompleteException implements Exception {
   String toString() => "Exception: future already completed";
 }
 
-/**
- * Wraps unhandled exceptions provided to [Completer.completeException]. It is
- * used to show both the error message and the stack trace for unhandled
- * exceptions.
- */
-class FutureUnhandledException implements Exception {
-  /** Wrapped exception. */
-  var source;
-
-  /** Trace for the wrapped exception. */
-  Object stackTrace;
-
-  FutureUnhandledException(this.source, this.stackTrace);
-
-  String toString() {
-    return 'FutureUnhandledException: exception while executing Future\n  '
-        '${source.toString().replaceAll("\n", "\n  ")}\n'
-        'original stack trace:\n  '
-        '${stackTrace.toString().replaceAll("\n","\n  ")}';
-  }
-}
-
 
 /**
  * [Futures] holds additional utility functions that operate on [Future]s (for