Hotfix undefined challenge_time

[dbobrenko]

Changes

• Revert PR with undefined HumanAgent.challenge_time: Raised an exception after trying 3 times to generate the challenge query #304

Problem Statement

13|otf-validator  |   File "/workspace/prompting/prompting/validator.py", line 53, in forward                                                                                     13|otf-validator  |     return await forward(self)
13|otf-validator  |   File "/workspace/prompting/prompting/forward.py", line 285, in forward
13|otf-validator  |     agent = HumanAgent(
13|otf-validator  |   File "/workspace/prompting/prompting/agent.py", line 87, in __init__
13|otf-validator  |     self.challenge = self.challenge_time()
13|otf-validator  | AttributeError: 'HumanAgent' object has no attribute 'challenge_time'

[Hollyqui]

LGTM