Remove unused ConnectionMgr (#2102)

Signed-off-by: Nxiaocai2333 <46207236+xiaocai2333@users.noreply.github.com>

shards/mishards/test_server.py

@@ -14,8 +14,6 @@ from mishards.service_handler import ServiceHandler
 from mishards.grpc_utils.grpc_args_parser import GrpcArgsParser as Parser
 from mishards.factories import TableFilesFactory, TablesFactory, TableFiles, Tables
 from mishards.router import RouterMixin
-from mishards.connections import (Connection,
-        ConnectionPool, ConnectionTopology, ConnectionGroup)
 
 logger = logging.getLogger(__name__)