Remove illegal const constructors.

Remove test of default constructor, which seems unnecessary.

Author: justinfagnani

lib/perf_api.dart

@@ -8,12 +8,6 @@ import 'dart:async';
 class Profiler {
   final Counters counters = new Counters();
 
-  /**
-   * Const constructor allows instances of this class to be used as a no-op
-   * implementation.
-   */
-  const Profiler();
-
   /**
    * Starts a new timer for a given action [name]. A timer id will be
    * returned which can be used in [stopTimer] to stop the timer.
@@ -73,8 +67,6 @@ class Counters {
 
   final Map<String, int> _counters = <String, int>{};
 
-  const Counters();
-
   /**
    * Increments the counter under [counterName] by [delta]. Default [delta]
    * is 1. If counter is not yet initilalized, its value is assumed to be 0.

test/perf_api_test.dart

@@ -7,10 +7,6 @@ import 'package:perf_api/perf_api.dart';
 
 main() {
 
-  test('should be able to instantiate as a noop profiler', () {
-    expect(() => new Profiler(), returnsNormally);
-  });
-
   group('Default Impl', () {
     Profiler perf;