Remove unused MonthRateTool import from test_tool_picker.py

test/test_tool_picker.py

@@ -7,7 +7,7 @@ from unittest.mock import Mock
 from langchain_openai import ChatOpenAI
 
 from src.server.tool_picker import ToolPicker
-from src.agent.tool_rate import RegionRateTool,RankingRateTool,MonthRateTool
+from src.agent.tool_rate import RegionRateTool,RankingRateTool
 from src.agent.tool_monitor import MonitorPointTool
 
 @pytest.fixture