fix: remove stdlib modules from requirements.txt

asyncio and uuid are Python standard library modules (available since
Python 3.4+). Listing them in requirements.txt is unnecessary and can
install unrelated PyPI packages with the same name, causing conflicts.

Affected files (8 total):
- starter_ai_agents: openai_research_agent, mixture_of_agents,
  ai_meme_generator_agent_browseruse
- mcp_ai_agents: github_mcp_agent, browser_mcp_agent
- ai_agent_framework_crash_course: 5_1_in_memory_conversation_agent,
  5_2_persistent_conversation_agent
- advanced_ai_agents: ai_financial_coach_agent