pkg/unittest: Removed references to expectAsync[Until]X in docs

pkg/unittest/lib/src/spread_args_helper.dart

 part of unittest;
 
 const _PLACE_HOLDER = const _ArgPlaceHolder();
 
 /// Used to track unused positional args.
 class _ArgPlaceHolder {
   const _ArgPlaceHolder();
 }
 
-/** Simulates spread arguments using named arguments. */
+/// Simulates spread arguments using named arguments.
 // TODO(sigmund): remove this class and simply use a closure with named
 // arguments (if still applicable).
 class _SpreadArgsHelper {
   final Function callback;
   final int minExpectedCalls;
   final int maxExpectedCalls;
   final Function isDone;
   final String id;
   int actualCalls = 0;
   final TestCase testCase;
@@ skipping 136 matching lines @@
   }
 }
 
 typedef _Func0();
 typedef _Func1(a);
 typedef _Func2(a, b);
 typedef _Func3(a, b, c);
 typedef _Func4(a, b, c, d);
 typedef _Func5(a, b, c, d, e);
 typedef _Func6(a, b, c, d, e, f);