test_cluster: remove import asyncore

this isn't being used anyhow, and breaking support
for python 3.12

Author: fruch

tests/integration/standard/test_cluster.py

@@ -11,7 +11,6 @@
 # WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 # See the License for the specific language governing permissions and
 # limitations under the License.
-import asyncore
 import subprocess
 
 import unittest