chore(config): remove the no-op analyst_concurrency_limit knob

The knob was accepted but inert — analysts run strictly sequentially and the
value was never used. Remove it rather than ship a misleading config key.
Parallel analyst execution is tracked for v0.3 (#634/#671/#487).

tradingagents/graph/trading_graph.py

@@ -110,7 +110,6 @@ class TradingAgentsGraph:
             self.deep_thinking_llm,
             self.tool_nodes,
             self.conditional_logic,
-            analyst_concurrency_limit=self.config.get("analyst_concurrency_limit", 1),
         )
 
         self.propagator = Propagator(