Remove unused imports, add pylint exceptions

src/python/grpcio/grpc/experimental/aio/_channel.py

@@ -391,6 +391,7 @@ class Channel:
         self._channel.closing()
 
         if grace:
+            # pylint: disable=unused-variable
             _, pending = await asyncio.wait(self._ongoing_calls.calls,
                                             timeout=grace,
                                             loop=self._loop)

src/python/grpcio_tests/tests_aio/unit/channel_test.py

@@ -15,13 +15,11 @@
 
 import logging
 import os
-import threading
 import unittest
 
 import grpc
 from grpc.experimental import aio
 from grpc.experimental.aio import _base_call
-from grpc.experimental.aio._channel import _OngoingCalls
 
 from src.proto.grpc.testing import messages_pb2, test_pb2_grpc
 from tests.unit.framework.common import test_constants

src/python/grpcio_tests/tests_aio/unit/close_channel_test.py

@@ -15,8 +15,6 @@
 
 import asyncio
 import logging
-import os
-import threading
 import unittest
 
 import grpc
@@ -25,24 +23,11 @@ from grpc.experimental.aio import _base_call
 from grpc.experimental.aio._channel import _OngoingCalls
 
 from src.proto.grpc.testing import messages_pb2, test_pb2_grpc
-from tests.unit.framework.common import test_constants
-from tests_aio.unit._constants import (UNARY_CALL_WITH_SLEEP_VALUE,
-                                       UNREACHABLE_TARGET)
+from tests_aio.unit._constants import UNARY_CALL_WITH_SLEEP_VALUE
 from tests_aio.unit._test_base import AioTestBase
 from tests_aio.unit._test_server import start_test_server
 
-_UNARY_CALL_METHOD = '/grpc.testing.TestService/UnaryCall'
 _UNARY_CALL_METHOD_WITH_SLEEP = '/grpc.testing.TestService/UnaryCallWithSleep'
-_STREAMING_OUTPUT_CALL_METHOD = '/grpc.testing.TestService/StreamingOutputCall'
-
-_INVOCATION_METADATA = (
-    ('initial-md-key', 'initial-md-value'),
-    ('trailing-md-key-bin', b'\x00\x02'),
-)
-
-_NUM_STREAM_RESPONSES = 5
-_REQUEST_PAYLOAD_SIZE = 7
-_RESPONSE_PAYLOAD_SIZE = 42
 
 
 class TestOngoingCalls(unittest.TestCase):