Fix tool propagation bug in hierarchical crews (#3679)

- Remove check_tools validator from task.py that was extending task.tools
  with agent.tools at creation time
- This caused manager agents in hierarchical crews to incorrectly inherit
  tools from task agents
- The crew.py execution logic already handles tool resolution correctly
  at execution time via fallback: task.tools or agent_to_use.tools or []
- Add reproduction test test_hierarchical_crew_does_not_propagate_agent_tools_to_manager
- Update test_task_tool_reflect_agent_tools to verify execution-time behavior

Fixes #3679

Co-Authored-By: João <joao@crewai.com>

src/crewai/task.py

@@ -336,12 +336,6 @@ class Task(BaseModel):
                 setattr(self, key, value)
         return self
 
-    @model_validator(mode="after")
-    def check_tools(self):
-        """Check if the tools are set."""
-        if not self.tools and self.agent and self.agent.tools:
-            self.tools.extend(self.agent.tools)
-        return self
 
     @model_validator(mode="after")
     def check_output(self):