Removed unused import from grpc.beta in tests

Author: mehrdada

src/python/grpcio_tests/tests/interop/methods.py

@@ -23,7 +23,6 @@
 from google.auth.transport import grpc as google_auth_transport_grpc
 from google.auth.transport import requests as google_auth_transport_requests
 import grpc
-from grpc.beta import implementations
 
 from src.proto.grpc.testing import empty_pb2
 from src.proto.grpc.testing import messages_pb2