Remove obsolete version of dromaeo

lib/html/benchmarks/dromaeo/tests/DomAttr.dart

-class Main {
-  static void main() {
-    final int num = 10240;
-
-    // Try to force real results.
-    var ret;
-    window.on.load.add((Event evt) {
-      Element elem = document.query('#test1');
-      Element a = document.query('a');
-
-      new Suite('dom-attr')
-        .test('getAttribute', void _() {
-          for (int i = 0; i < num; i++)
-            ret = elem.attributes['id'];
-        })
-        .test('element.property', () {
-          for (int i = 0; i < num * 2; i++)
-            ret = elem.id;
-        })
-        .test('setAttribute', () {
-          for (int i = 0; i < num; i++)
-            a.attributes['id'] = 'foo';
-        })
-        .test('element.property = value', () {
-          for (int i = 0; i < num; i++)
-            a.id = 'foo';
-        })
-        .end();
-    });
-  }
-}