Revert "[VS test] Skip flaky virtual chassis test (sonic-net#2004)"

This reverts commit facdef5.

With the changes in platfrom/vs/docker-sonic-vs/start.sh done via
sonic-buildimage PR sonic-net/sonic-buildimage#8008
all tests will pass. No need to skip the tests.

So reverting this commit

tests/test_virtual_chassis.py

@@ -603,7 +603,6 @@ def test_chassis_system_lag(self, vct):
 
                     break
 
-    @pytest.mark.skip(reason="This test is not stable enough")
     def test_chassis_system_lag_id_allocator_table_full(self, vct):
         """Test lag id allocator table full.
         
@@ -681,7 +680,6 @@ def test_chassis_system_lag_id_allocator_table_full(self, vct):
 
                     break
 
-    @pytest.mark.skip(reason="This test is not stable enough")
     def test_chassis_system_lag_id_allocator_del_id(self, vct):
         """Test lag id allocator's release id and re-use id processing.